Showing papers on "Magnetoresistance published in 2016"
TL;DR: This work establishes the detailed Fermi-surface topology of the recently identified WSM TaP via combined angle-resolved quantum-oscillation spectra and band-structure calculations and observes a large negative longitudinal magnetoresistance.
Abstract: Weyl semimetals (WSMs) are topological quantum states wherein the electronic bands disperse linearly around pairs of nodes with fixed chirality, the Weyl points In WSMs, nonorthogonal electric and magnetic fields induce an exotic phenomenon known as the chiral anomaly, resulting in an unconventional negative longitudinal magnetoresistance, the chiral-magnetic effect However, it remains an open question to which extent this effect survives when chirality is not well-defined Here, we establish the detailed Fermi-surface topology of the recently identified WSM TaP via combined angle-resolved quantum-oscillation spectra and band-structure calculations The Fermi surface forms banana-shaped electron and hole pockets surrounding pairs of Weyl points Although this means that chirality is ill-defined in TaP, we observe a large negative longitudinal magnetoresistance We show that the magnetoresistance can be affected by a magnetic field-induced inhomogeneous current distribution inside the sample
1,389 citations
TL;DR: A magnetotransport study of zirconium pentatelluride, ZrTe5, has been carried out in this paper, which reveals evidence for a chiral magnetic effect, a striking macroscopic manifestation of the quantum and relativistic nature of Weyl semimetals.
Abstract: A magnetotransport study of zirconium pentatelluride now reveals evidence for a chiral magnetic effect, a striking macroscopic manifestation of the quantum and relativistic nature of Weyl semimetals The chiral magnetic effect is the generation of an electric current induced by chirality imbalance in the presence of a magnetic field It is a macroscopic manifestation of the quantum anomaly1,2 in relativistic field theory of chiral fermions (massless spin 1/2 particles with a definite projection of spin on momentum)—a remarkable phenomenon arising from a collective motion of particles and antiparticles in the Dirac sea The recent discovery3,4,5,6 of Dirac semimetals with chiral quasiparticles opens a fascinating possibility to study this phenomenon in condensed matter experiments Here we report on the measurement of magnetotransport in zirconium pentatelluride, ZrTe5, that provides strong evidence for the chiral magnetic effect Our angle-resolved photoemission spectroscopy experiments show that this material’s electronic structure is consistent with a three-dimensional Dirac semimetal We observe a large negative magnetoresistance when the magnetic field is parallel with the current The measured quadratic field dependence of the magnetoconductance is a clear indication of the chiral magnetic effect The observed phenomenon stems from the effective transmutation of a Dirac semimetal into a Weyl semimetal induced by parallel electric and magnetic fields that represent a topologically non-trivial gauge field background We expect that the chiral magnetic effect may emerge in a wide class of materials that are near the transition between the trivial and topological insulators
806 citations
TL;DR: The observation of NMR in Cd3As2 microribbons in parallel magnetic fields up to 66% at 50 K and visible at room temperatures is reported, demonstrating the chiral anomaly, a long-sought high-energy-physics effect, in solid-state systems.
Abstract: A large negative magnetoresistance (NMR) is anticipated in topological semimetals in parallel magnetic fields, demonstrating the chiral anomaly, a long-sought high-energy-physics effect, in solid-state systems. Recent experiments reveal that the Dirac semimetal Cd3As2 has the record-high mobility and positive linear magnetoresistance in perpendicular magnetic fields. However, the NMR has not yet been unveiled. Here we report the observation of NMR in Cd3As2 microribbons in parallel magnetic fields up to 66% at 50 K and visible at room temperatures. The NMR is sensitive to the angle between magnetic and electrical fields, robust against temperature and dependent on the carrier density. The large NMR results from low carrier densities in our Cd3As2 samples, ranging from 3.0 × 10(17) cm(-3) at 300 K to 2.2 × 10(16) cm(-3) below 50 K. We therefore attribute the observed NMR to the chiral anomaly. In perpendicular magnetic fields, a positive linear magnetoresistance up to 1,670% at 14 T and 2 K is also observed.
398 citations
TL;DR: 1T-TiSe2 single crystals with thicknesses of 10 nanometres or less, encapsulated in two-dimensional layers of hexagonal boron nitride, are studied to achieve unprecedented control over the CDW transition temperature, and over the superconductivity transition temperature.
Abstract: To understand the complex physics of a system with strong electron-electron interactions, the ideal is to control and monitor its properties while tuning an external electric field applied to the system (the electric-field effect). Indeed, complete electric-field control of many-body states in strongly correlated electron systems is fundamental to the next generation of condensed matter research and devices. However, the material must be thin enough to avoid shielding of the electric field in the bulk material. Two-dimensional materials do not experience electrical screening, and their charge-carrier density can be controlled by gating. Octahedral titanium diselenide (1T-TiSe2) is a prototypical two-dimensional material that reveals a charge-density wave (CDW) and superconductivity in its phase diagram, presenting several similarities with other layered systems such as copper oxides, iron pnictides, and crystals of rare-earth elements and actinide atoms. By studying 1T-TiSe2 single crystals with thicknesses of 10 nanometres or less, encapsulated in two-dimensional layers of hexagonal boron nitride, we achieve unprecedented control over the CDW transition temperature (tuned from 170 kelvin to 40 kelvin), and over the superconductivity transition temperature (tuned from a quantum critical point at 0 kelvin up to 3 kelvin). Electrically driving TiSe2 over different ordered electronic phases allows us to study the details of the phase transitions between many-body states. Observations of periodic oscillations of magnetoresistance induced by the Little-Parks effect show that the appearance of superconductivity is directly correlated with the spatial texturing of the amplitude and phase of the superconductivity order parameter, corresponding to a two-dimensional matrix of superconductivity. We infer that this superconductivity matrix is supported by a matrix of incommensurate CDW states embedded in the commensurate CDW states. Our results show that spatially modulated electronic states are fundamental to the appearance of two-dimensional superconductivity.
365 citations
TL;DR: A series of transport experiments on lanthanum antimonide reveal a plateau in its resistivity and an extremely large magnetoresistance that are consistent with topologically protected electronic states as mentioned in this paper.
Abstract: A series of transport experiments on lanthanum antimonide reveal a plateau in its resistivity and an extremely large magnetoresistance that are consistent with topologically protected electronic states.
297 citations
TL;DR: A model is developed to account for the absorption of the longitudinal spin current to the FM layer, one of the key characteristics of a metallic ferromagnet, and finds a nearly tenfold increase of SMR in W/CoFeB compared to previously studied HM/ferromagnetic insulator systems.
Abstract: Spin Hall magnetoresistance (SMR) is studied in metallic bilayers that consist of a heavy metal (HM) layer and a ferromagnetic metal (FM) layer. We find a nearly tenfold increase of SMR in $\mathrm{W}/\mathrm{CoFeB}$ compared to previously studied HM/ferromagnetic insulator systems. The SMR increases with decreasing temperature despite the negligible change in the W layer resistivity. A model is developed to account for the absorption of the longitudinal spin current to the FM layer, one of the key characteristics of a metallic ferromagnet. We find that the model not only quantitatively describes the HM layer thickness dependence of SMR, allowing accurate estimation of the spin Hall angle and the spin diffusion length of the HM layer, but also can account for the temperature dependence of SMR by assuming a temperature dependent spin polarization of the FM layer. These results illustrate the unique role a metallic ferromagnetic layer plays in defining spin transmission across the $\mathrm{HM}/\mathrm{FM}$ interface.
290 citations
TL;DR: Chiral helicene, a fully conjugated system without stereogenic carbon, can filter spins effectively at room temperature, a consequence of the chiral-induced spin-selectivity effect.
Abstract: Chiral helicene, a fully conjugated system without stereogenic carbon, can filter spins effectively at room temperature, a consequence of the chiral-induced spin-selectivity effect. The chirality dictates the spin of the electrons transferred through helicene, and magnetoresistance devices based on these molecules show antisymmetric magnetoresistance versus H plots.
265 citations
TL;DR: By performing systematic magneto-transport studies on thin films of a predicted material candidate WTe2, this work observes notable negative longitudinal magnetoresistance, which can be attributed to the chiral anomaly in WSM and demonstrates that the Fermi energy can be in-situ tuned through the Weyl points via the electric field effect.
Abstract: The progress in exploiting new electronic materials has been a major driving force in solid-state physics. As a new state of matter, a Weyl semimetal (WSM), in particular a type-II WSM, hosts Weyl fermions as emergent quasiparticles and may harbour novel electrical transport properties. Nevertheless, such a type-II WSM material has not been experimentally observed. In this work, by performing systematic magneto-transport studies on thin films of a predicted material candidate WTe2, we observe notable negative longitudinal magnetoresistance, which can be attributed to the chiral anomaly in WSM. This phenomenon also exhibits strong planar orientation dependence with the absence along the tungsten chains, consistent with the distinctive feature of a type-II WSM. By applying a gate voltage, we demonstrate that the Fermi energy can be in-situ tuned through the Weyl points via the electric field effect. Our results may open opportunities for implementing new electronic applications, such as field-effect chiral devices.
254 citations
TL;DR: A multiple-stable memory device in epitaxial MnTe, an antiferromagnetic counterpart of common II–VI semiconductors, is demonstrated, demonstrating the robustness against strong magnetic field perturbations combined with the multiple stability of the magnetic memory states.
Abstract: Commercial magnetic memories rely on the bistability of ordered spins in ferromagnetic materials. Recently, experimental bistable memories have been realized using fully compensated antiferromagnetic metals. Here we demonstrate a multiple-stable memory device in epitaxial MnTe, an antiferromagnetic counterpart of common II–VI semiconductors. Favourable micromagnetic characteristics of MnTe allow us to demonstrate a smoothly varying zero-field antiferromagnetic anisotropic magnetoresistance (AMR) with a harmonic angular dependence on the writing magnetic field angle, analogous to ferromagnets. The continuously varying AMR provides means for the electrical read-out of multiple-stable antiferromagnetic memory states, which we set by heat-assisted magneto-recording and by changing the writing field direction. The multiple stability in our memory is ascribed to different distributions of domains with the Neel vector aligned along one of the three magnetic easy axes. The robustness against strong magnetic field perturbations combined with the multiple stability of the magnetic memory states are unique properties of antiferromagnets. Contrary to ferromagnets, antiferromagnets possess no net magnetic moment, which has limited their applicability as magnetic memory media. Here, the authors demonstrate a heat-assisted multiple-stable memory based on epitaxial thin films of antiferromagnet MnTe with three-fold symmetric anisotropy.
188 citations
TL;DR: The observation of an unusual “butterfly”-shaped titanic angular magnetoresistance (AMR) in the nonmagnetic Dirac material, ZrSiS, which is found to be the most conducting sulfide known, with a 2-K resistivity as low as 48(4) nΩ⋅cm is reported.
Abstract: Magnetoresistance (MR), the change of a material's electrical resistance in response to an applied magnetic field, is a technologically important property that has been the topic of intense study for more than a quarter century. We report the observation of an unusual "butterfly"-shaped titanic angular magnetoresistance (AMR) in the nonmagnetic Dirac material, ZrSiS, which we find to be the most conducting sulfide known, with a 2-K resistivity as low as 48(4) nΩ⋅cm. The MR in ZrSiS is large and positive, reaching nearly 1.8 × 105 percent at 9 T and 2 K at a 45° angle between the applied current (I || a) and the applied field (90° is H || c). Approaching 90°, a "dip" is seen in the AMR, which, by analyzing Shubnikov de Haas oscillations at different angles, we find to coincide with a very sharp topological phase transition unlike any seen in other known Dirac/Weyl materials. We find that ZrSiS has a combination of two-dimensional (2D) and 3D Dirac pockets comprising its Fermi surface and that the combination of high-mobility carriers and multiple pockets in ZrSiS allows for large property changes to occur as a function of angle between applied fields. This makes it a promising platform to study the physics stemming from the coexistence of 2D and 3D Dirac electrons as well as opens the door to creating devices focused on switching between different parts of the Fermi surface and different topological states.
179 citations
TL;DR: The large magnitude of UMR is an outcome of spin-momentum locking and a small Fermi wave number at the surface of TI, and the UMR was identified to originate from the asymmetric scattering of electrons by magnons.
Abstract: We report current-direction dependent or unidirectional magnetoresistance (UMR) in magnetic or nonmagnetic topological insulator (TI) heterostructures, Cr_{x}(Bi_{1-y}Sb_{y})_{2-x}Te_{3}/(Bi_{1-y}Sb_{y})_{2}Te_{3}, that is several orders of magnitude larger than in other reported systems. From the magnetic field and temperature dependence, the UMR is identified to originate from the asymmetric scattering of electrons by magnons. In particular, the large magnitude of UMR is an outcome of spin-momentum locking and a small Fermi wave number at the surface of TI. In fact, the UMR is maximized around the Dirac point with the minimal Fermi wave number.
TL;DR: In this paper, the authors present experimental evidence that the observation of the chiral anomaly can be hindered by an effect called "current jetting", which is characterized by a highly non-uniform current distribution inside the sample.
Abstract: Recently, the existence of massless chiral (Weyl) fermions has been postulated in a class of semi-metals with a non-trivial energy dispersion. These materials are now commonly dubbed Weyl semi-metals (WSM). One predicted property of Weyl fermions is the chiral or Adler–Bell–Jackiw anomaly, a chirality imbalance in the presence of parallel magnetic and electric fields. In WSM, it is expected to induce a negative longitudinal magnetoresistance (MR). Here, we present experimental evidence that the observation of the chiral anomaly can be hindered by an effect called 'current jetting'. This effect also leads to a strong apparent negative longitudinal MR, but it is characterized by a highly non-uniform current distribution inside the sample. It appears in materials possessing a large field-induced anisotropy of the resistivity tensor, such as almost compensated high-mobility semimetals due to the orbital effect. In case of a non-homogeneous current injection, the potential distribution is strongly distorted in the sample. As a consequence, an experimentally measured potential difference is not proportional to the intrinsic resistance. Our results on the MR of the Weyl semimetal candidate materials NbP, NbAs, TaAs, and TaP exhibit distinct signatures of an inhomogeneous current distribution, such as a field-induced 'zero resistance' and a strong dependence of the 'measured resistance' on the position, shape, and type of the voltage and current contacts on the sample. A misalignment between the current and the magnetic-field directions can even induce a 'negative resistance'. Finite-element simulations of the potential distribution inside the sample, using typical resistance anisotropies, are in good agreement with the experimental findings. Our study demonstrates that great care must be taken before interpreting measurements of a negative longitudinal MR as evidence for the chiral anomaly in putative Weyl semimetals.
TL;DR: In this paper, an anomalous Hall effect (AHE) was detected for every sample, with no magnetic ordering observed in the system to the experimental sensitivity of torque magnetometry.
Abstract: ZrTe$_5$ has been of recent interest as a potential Dirac/Weyl semimetal material. Here, we report the results of experiments performed via in-situ 3D double-axis rotation to extract the full $4\pi$ solid angular dependence of the transport properties. A clear anomalous Hall effect (AHE) was detected for every sample, with no magnetic ordering observed in the system to the experimental sensitivity of torque magnetometry. Interestingly, the AHE takes large values when the magnetic field is rotated in-plane, with the values vanishing above $\sim 60$ K where the negative longitudinal magnetoresistance (LMR) also disappears. This suggests a close relation in their origins, which we attribute to Berry curvature generated by the Weyl nodes.
TL;DR: It is concluded that 2D electrons in those structures in moderate magnetic fields should be treated as a viscous fluid, which is responsible for the giant negative magnetoresistance recently observed in the ultrahigh-mobility GaAs quantum wells.
Abstract: At low temperatures, in very clean two-dimensional (2D) samples, the electron mean free path for collisions with static defects and phonons becomes greater than the sample width. Under this condition, the electron transport occurs by formation of a viscous flow of an electron fluid. We study the viscous flow of 2D electrons in a magnetic field perpendicular to the 2D layer. We calculate the viscosity coefficients as the functions of magnetic field and temperature. The off-diagonal viscosity coefficient determines the dispersion of the 2D hydrodynamic waves. The decrease of the diagonal viscosity in magnetic field leads to negative magnetoresistance which is temperature and size dependent. Our analysis demonstrates that this viscous mechanism is responsible for the giant negative magnetoresistance recently observed in the ultrahigh-mobility GaAs quantum wells. We conclude that 2D electrons in those structures in moderate magnetic fields should be treated as a viscous fluid.
TL;DR: In this paper, the 3D Dirac semimetal phase of layered material was shown to be a 3D massless Dirac and Weyl fermions in a layered compound.
Abstract: Topological Dirac semimetal is a newly discovered class of materials which has attracted intense attention. This material can be viewed as a three-dimensional (3D) analog of graphene and has linear energy dispersion in bulk, leading to a range of exotic transport properties. Here we report direct quantum transport evidence of the 3D Dirac semimetal phase of layered material $\mathrm{ZrT}{\mathrm{e}}_{5}$ by angular-dependent magnetoresistance measurements under high magnetic fields up to 31 T. We observed very clear negative longitudinal magnetoresistance induced by chiral anomaly under the condition of the magnetic field aligned only along the current direction. Pronounced Shubnikov--de Hass (SdH) quantum oscillations in both longitudinal magnetoresistance and transverse Hall resistance were observed, revealing anisotropic light cyclotron masses and high mobility of the system. In particular, a nontrivial \ensuremath{\pi}-Berry phase in the SdH oscillations gives clear evidence for the 3D Dirac semimetal phase. Furthermore, we observed clear Landau level splitting under high magnetic field, suggesting possible splitting of the Dirac point into Weyl points due to broken time-reversal symmetry. Our results indicate that $\mathrm{ZrT}{\mathrm{e}}_{5}$ is an ideal platform to study 3D massless Dirac and Weyl fermions in a layered compound.
TL;DR: In this article, the authors measured the high-field magnetoresistance of the iron pnictide superconductor BaFe2(As 1−xPx)2 and found that it obeys an unusual scaling relationship between applied magnetic field and temperature, with a conversion factor given simply by the ratio of the Bohr magneton and the Boltzmann constant.
Abstract: The linear change in resistance with temperature in high-temperature superconductors is an enduring mystery. And now, the resistance in a magnetic field shows similar scaling, suggesting that physicists have another probe of the linear behaviour. Many exotic metallic systems have a resistivity that varies linearly with temperature, and the physics behind this is thought to be connected to high-temperature superconductivity in the cuprates and iron pnictides1,2,3,4,5,6,7,8,9. Although this phenomenon has attracted considerable attention, it is unclear how the relevant physics manifests in other transport properties, for example their response to an applied magnetic field. We report measurements of the high-field magnetoresistance of the iron pnictide superconductor BaFe2(As1−xPx)2 and find that it obeys an unusual scaling relationship between applied magnetic field and temperature, with a conversion factor given simply by the ratio of the Bohr magneton and the Boltzmann constant. This suggests that magnetic fields probe the same physics that gives rise to the T-linear resistivity, providing a new experimental clue to this long-standing puzzle.
TL;DR: It is shown that this Hanle magnetoresistance is an alternative simple way to quantitatively study the coupling between charge and spin currents in metals with strong spin-orbit coupling.
Abstract: We report measurements of a new type of magnetoresistance in Pt and Ta thin films. The spin accumulation created at the surfaces of the film by the spin Hall effect decreases in a magnetic field because of the Hanle effect, resulting in an increase of the electrical resistance as predicted by Dyakonov [Phys. Rev. Lett. 99, 126601 (2007)]. The angular dependence of this magnetoresistance resembles the recently discovered spin Hall magnetoresistance in Pt/Y(3)Fe(5)O(12) bilayers, although the presence of a ferromagnetic insulator is not required. We show that this Hanle magnetoresistance is an alternative simple way to quantitatively study the coupling between charge and spin currents in metals with strong spin-orbit coupling.
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TL;DR: In this article, an anomalous titanic angular magnetoresistance (AMR) was observed in the non-magnetic, Dirac material, ZrSiS, at an angle of 45o between the applied current (along the a-axis) and the applied field (90o is H parallel to the c-axis).
Abstract: Magnetoresistance (MR), the change of a material's electrical resistance in response to an applied magnetic field, is a technologically important property that has been the topic of intense study for more than a quarter century. Here we report the observation of an unusual "butterfly" shaped titanic angular magnetoresistance (AMR) in the non-magnetic, Dirac material, ZrSiS. The MR is large and positive, reaching nearly 1.8 x 10^5 percent at 9 T and 2 K at an angle of 45o between the applied current (along the a-axis) and the applied field (90o is H parallel to the c-axis). Approaching 90o, a "dip" is seen in the AMR which can be traced to an angle dependent deviation from the H^2 law. By analyzing the SdH oscillations at different angles, we find that ZrSiS has a combination of 2D and 3D Dirac pockets comprising its Fermi surface and that the anomalous transport behavior coincides with a topological phase transition whose robust signature is evident despite transport contributions from other parts of the Fermi surface. We also find that as a function of angle, the temperature dependent resistivity in high field displays a broad peak-like behavior, unlike any known Dirac/Weyl material. The combination of very high mobility carriers and multiple Fermi surfaces in ZrSiS allow for large bulk property changes to occur as a function of angle between applied fields makes it a promising platform to study the physics stemming from the coexistence of 2D and 3D Dirac electrons.
TL;DR: By combining angle-resolved photoemission spectroscopy and quantum oscillation measurements, a comprehensive investigation on the electronic structure of LaSb is performed, which exhibits near-quadratic extremely large magnetoresistance (XMR) without any sign of saturation at magnetic fields as high as 40 T.
Abstract: By combining angle-resolved photoemission spectroscopy and quantum oscillation measurements, we performed a comprehensive investigation on the electronic structure of LaSb, which exhibits near-quadratic extremely large magnetoresistance (XMR) without any sign of saturation at magnetic fields as high as 40 T. We clearly resolve one spherical and one intersecting-ellipsoidal hole Fermi surfaces (FSs) at the Brillouin zone (BZ) center $\mathrm{\ensuremath{\Gamma}}$ and one ellipsoidal electron FS at the BZ boundary $X$. The hole and electron carriers calculated from the enclosed FS volumes are perfectly compensated, and the carrier compensation is unaffected by temperature. We further reveal that LaSb is topologically trivial but shares many similarities with the Weyl semimetal TaAs family in the bulk electronic structure. Based on these results, we have examined the mechanisms that have been proposed so far to explain the near-quadratic XMR in semimetals.
TL;DR: The chiral soliton lattice appears under a magnetic field perpendicular to the chiral helical axis and is very robust and stable with phase coherence on a macroscopic length scale as discussed by the authors.
Abstract: Nontrivial spin orders with magnetic chirality emerge in a particular class of magnetic materials with structural chirality, which are frequently referred to as chiral magnets. Various interesting physical properties are expected to be induced in chiral magnets through the coupling of chiral magnetic orders with conduction electrons and electromagnetic fields. One promising candidate for achieving these couplings is a chiral spin soliton lattice. Here, we review recent experimental observations mainly carried out on the monoaxial chiral magnetic crystal CrNb3S6 via magnetic imaging using electron, neutron, and X-ray beams and magnetoresistance measurements, together with the strategy for synthesizing chiral magnetic materials and underlying theoretical backgrounds. The chiral soliton lattice appears under a magnetic field perpendicular to the chiral helical axis and is very robust and stable with phase coherence on a macroscopic length scale. The tunable and topological nature of the chiral soliton lattic...
TL;DR: Song et al. as mentioned in this paper proposed a new method to solve the problem of high magnetic field field and showed that the method can be applied in the field of particle physics, which can achieve state-of-the-art performance.
Abstract: Prof. X. F. Wang, M. Gao, J. R. Zhang, M. H. Zhang, W. Niu, Prof. Y. B. Xu, Prof. R. Zhang National Laboratory of Solid State Microstructures Collaborative Innovation Center of Advanced Microstructures School of Electronic Science and Engineering Nanjing University Nanjing 210093, P. R. China E-mail: xfwang@nju.edu.cn; rzhang@nju.edu.cn X. C. Pan, J. H. Yu, Z. X. Wei, Prof. X. G. Wan, Prof. F. Q. Song, Prof. B. G. Wang, Prof. G. H. Wang School of Physics Nanjing University Nanjing 210093, P. R. China E-mail: songfengqi@nju.edu.cn Dr. J. Jiang, Prof. Y. L. Chen School of Physical Science and Technology ShanghaiTech University CAS-Shanghai Science Research Center Shanghai 200031, P. R. China Dr. H. K. Zuo, Prof. Z. C. Xia Wuhan National High Magnetic Field Center Huazhong University of Science and Technology Wuhan 430074, P. R. China
TL;DR: It is found that, even when the magnetization is saturated, the resistance increases with increasing the magnetic-field strength, which is attributed to the Hanle magnetoresistance in this system.
Abstract: We report the observation of magnetoresistance originating from Rashba spin-orbit coupling (SOC) in a metallic heterostructure: the Rashba-Edelstein (RE) magnetoresistance. We show that the simultaneous action of the direct and inverse RE effects in a $\mathrm{Bi}/\mathrm{Ag}/\mathrm{CoFeB}$ trilayer couples current-induced spin accumulation to the electric resistance. The electric resistance changes with the magnetic-field angle, reminiscent of the spin Hall magnetoresistance, despite the fact that bulk SOC is not responsible for the magnetoresistance. We further found that, even when the magnetization is saturated, the resistance increases with increasing the magnetic-field strength, which is attributed to the Hanle magnetoresistance in this system.
TL;DR: A highly sensitive flexible magnetic sensor based on the anisotropic magnetoresistance effect is fabricated and excellent deformation stability is achieved after wrapping of the flexible sensor, with bending radii down to 5 mm.
Abstract: A highly sensitive flexible magnetic sensor based on the anisotropic magnetoresistance effect is fabricated. A limit of detection of 150 nT is observed and excellent deformation stability is achieved after wrapping of the flexible sensor, with bending radii down to 5 mm. The flexible AMR sensor is used to read a magnetic pattern with a thickness of 10 μm that is formed by ferrite magnetic inks.
TL;DR: In this paper, the integration of atomically thin 2D insulating hexagonal boron nitride tunnel barriers into Co/h-BN/Fe magnetic tunnel junctions (MTJ) is described.
Abstract: We report on the integration of atomically thin 2D insulating hexagonal boron nitride (h-BN) tunnel barriers into Co/h-BN/Fe magnetic tunnel junctions(MTJs). The h-BN monolayer is directly grown by chemical vapor deposition on Fe. The Conductive Tip Atomic Force Microscopy (CT-AFM) measurements reveal the homogeneity of the tunnel behavior of our h-BN layers. As expected for tunneling, the resistance depends exponentially on the number of h-BN layers. The h-BN monolayer properties are also characterized through integration into complete MTJ devices. A Tunnel Magnetoresistance of up to 6% is observed for a MTJ based on a single atomically thin h-BN layer.
TL;DR: In this paper, high quality single crystals of NbAs2/TaAs2 with inversion symmetry have been grown and the resistivity under magnetic field was systematically investigated, and a metal-to-insulator transition occurs when a nonzero magnetic field is applied.
Abstract: In topological insulators (TIs), metallic surface conductance saturates the insulating bulk resistance with de- creasing temperature, resulting in resistivity plateau at low temperatures as a transport signature originating from metallic surface modes protected by time reversal symmetry (TRS). Such characteristic has been found in several materials including Bi2Te2Se, SmB6 etc. Recently, similar behavior has been observed in metallic com- pound LaSb, accompanying an extremely large magetoresistance (XMR). Shubnikov-de Hass (SdH) oscillation at low temperatures further confirms the metallic behavior of plateau region under magnetic fields. LaSb[1] has been proposed by the authors as a possible topological semimetal (TSM), while negative magnetoresistance is absent at this moment. Here, high quality single crystals of NbAs2/TaAs2 with inversion symmetry have been grown and the resistivity under magnetic field is systematically investigated. Both of them exhibit metallic behavior under zero magnetic field, and a metal-to-insulator transition occurs when a nonzero magnetic field is applied, resulting in XMR (1.0*105% for NbAs2 and 7.3*105% for TaAs2 at 2.5 K & 14 T). With tempera- ture decreased, a resistivity plateau emerges after the insulator-like regime and SdH oscillation has also been observed in NbAs2 and TaAs2.
TL;DR: It is suggested that XMR in LaBi and LaSb originates from a combination of compensated electron−hole pockets and a particular orbital texture on the electron pocket, which is likely to be a generic feature of various topological semimetals, giving rise to their small residual resistivity at zero field and subject to strong scattering induced by a magnetic field.
Abstract: The recent discovery of extreme magnetoresistance (XMR) in LaSb introduced lanthanum monopnictides as a new platform to study this effect in the absence of broken inversion symmetry or protected linear band crossing. In this work, we report XMR in LaBi. Through a comparative study of magnetotransport effects in LaBi and LaSb, we construct a temperature−field phase diagram with triangular shape that illustrates how a magnetic field tunes the electronic behavior in these materials. We show that the triangular phase diagram can be generalized to other topological semimetals with different crystal structures and different chemical compositions. By comparing our experimental results to band structure calculations, we suggest that XMR in LaBi and LaSb originates from a combination of compensated electron−hole pockets and a particular orbital texture on the electron pocket. Such orbital texture is likely to be a generic feature of various topological semimetals, giving rise to their small residual resistivity at zero field and subject to strong scattering induced by a magnetic field.
TL;DR: Comprehensive characterization of Raman spectra of WTe2 from bulk to monolayer using experimental and computational methods is reported and it is found that mono and bi-layer W Te2 are easily identified by Raman Spectroscopy since two or one Raman modes that are observed in higher-layerWTe2 are greatly suppressed below the noise level in the mono- andBi- layer WTe1.
Abstract: Tungsten ditelluride (WTe2) is a layered material that exhibits excellent magnetoresistance and thermoelectric behaviors, which are deeply related with its distorted orthorhombic phase that may critically affect the lattice dynamics of this material. Here, we report comprehensive characterization of Raman spectra of WTe2 from bulk to monolayer using experimental and computational methods. We find that mono and bi-layer WTe2 are easily identified by Raman spectroscopy since two or one Raman modes that are observed in higher-layer WTe2 are greatly suppressed below the noise level in the mono- and bi-layer WTe2, respectively. In addition, the frequency of in-plane A17 mode of WTe2 remains almost constant as the layer number decreases, while all the other Raman modes consistently blueshift, which is completely different from the vibrational behavior of hexagonal metal dichalcogenides. First-principles calculation validates experimental results and reveals that anomalous lattice vibrations in WTe2 are attributed to the formation of tungsten chains that make WTe2 structurally one-dimensional.
TL;DR: This work demonstrates that chiral imprinted CdSe quantum dots (QDs) can act as spin selective filters for charge transport and may prove useful in future applications, for example, photovoltaics, spintronics, and other spin-driven devices.
Abstract: This work demonstrates that chiral imprinted CdSe quantum dots (QDs) can act as spin selective filters for charge transport. The spin filtering properties of chiral nanoparticles were investigated by magnetic conductive-probe atomic force microscopy (mCP-AFM) measurements and magnetoresistance measurements. The mCP-AFM measurements show that the chirality of the quantum dots and the magnetic orientation of the tip affect the current–voltage curves. Similarly, magnetoresistance measurements demonstrate that the electrical transport through films of chiral quantum dots correlates with the chiroptical properties of the QD. The spin filtering properties of chiral quantum dots may prove useful in future applications, for example, photovoltaics, spintronics, and other spin-driven devices.
TL;DR: The EEI effect can be used to analyze the coupling effect between the top and bottom surface states in topological insulator like the WAL effect, which is two dimensional in nature.
Abstract: We study the low-temperature transport properties of Bi2Se3 thin films grown by magnetron sputtering. A positive magnetoresistance resulting from the weak antilocalization (WAL) effect is observed at low temperatures. The observed WAL effect is two dimensional in nature. Applying the Hikami-Larkin-Nagaoka theory, we have obtained the dephasing length. It is found that the temperature dependence of the dephasing length cannot be described only by the Nyquist electron-electron dephasing, in conflict with prevailing experimental results. From the WAL effect, we extract the number of the transport channels, which is found to increase with increasing the thickness of the films, reflecting the thickness-dependent coupling between the top and bottom surface states in topological insulator. On the other hand, the electron-electron interaction (EEI) effect is observed in temperature-dependent conductivity. From the EEI effect, we also extract the number of the transport channel, which shows similar thickness dependence with that obtained from the analysis of the WAL effect. The EEI effect, therefore, can be used to analyze the coupling effect between the top and bottom surface states in topological insulator like the WAL effect.
TL;DR: In this article, a semimetal with a band inversion equivalent to a topological insulator was observed to exhibit surface-state-like behavior in the magnetoresistance, where the electrons responsible for this pseudo-two-dimensional transport originate from the bulk states rather topological surface states.
Abstract: Topological insulators are characterized by an inverted band structure in the bulk and metallic surface states on the surface. In LaBi, a semimetal with a band inversion equivalent to a topological insulator, we observe surface-state-like behavior in the magnetoresistance. The electrons responsible for this pseudo-two-dimensional transport, however, originate from the bulk states rather topological surface states, which is witnessed by the angle-dependent quantum oscillations of the magnetoresistance and ab initio calculations. As a consequence, the magnetoresistance exhibits strong anisotropy with large amplitude $(\ensuremath{\sim}{10}^{5}%)$.