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Tsz Chun Wu

Bio: Tsz Chun Wu is an academic researcher from Rice University. The author has contributed to research in topics: Physics & Superconductivity. The author has an hindex of 3, co-authored 4 publications receiving 21 citations.

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TL;DR: In this article, the authors show that a Weyl superconductor can absorb light via a surface-to-bulk mechanism, which they dub the topological anomalous skin effect.
Abstract: We show that a Weyl superconductor can absorb light via a novel surface-to-bulk mechanism, which we dub the topological anomalous skin effect. This occurs even in the absence of disorder for a single-band superconductor, and is facilitated by the topological splitting of the Hilbert space into bulk and chiral surface Majorana states. In the clean limit, the effect manifests as a characteristic absorption peak due to surface-bulk transitions. We also consider the effects of bulk disorder, using the Keldysh response theory. For weak disorder, the bulk response is reminiscent of the Mattis-Bardeen result for $s$-wave superconductors, with strongly suppressed spectral weight below twice the pairing energy, despite the presence of gapless Weyl points. For stronger disorder, the bulk response becomes more Drude-like and the $p$-wave features disappear. We show that the surface-bulk signal survives when combined with the bulk in the presence of weak disorder. The topological anomalous skin effect can therefore serve as a fingerprint for Weyl superconductivity. We also compute the Meissner response in the slab geometry, incorporating the effect of the surface states.

13 citations

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TL;DR: In this paper, the temperature dependence of the magnetic penetration depth in a 3D topological superconductor (TSC), incorporating the paramagnetic current due to the surface states, was studied.
Abstract: We study the temperature dependence of the magnetic penetration depth in a 3D topological superconductor (TSC), incorporating the paramagnetic current due to the surface states. A TSC is predicted to host a gapless 2D surface Majorana fluid. In addition to the bulk-dominated London response, we identify a ${T}^{3}$ power-law-in-temperature contribution from the surface, valid in the low-temperature limit. Our system is fully gapped in the bulk, and should be compared to bulk nodal superconductivity, which also exhibits power-law behavior. Power-law temperature dependence of the penetration depth can be one indicator of topological superconductivity.

7 citations

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TL;DR: In this paper, the authors present a systematic tunneling spectroscopy study, over a broad doping, temperature, and bias range, in epitaxial $c$-axis.
Abstract: Atomically precise epitaxial structures are unique systems for tunneling spectroscopy that minimize extrinsic effects of disorder. We present a systematic tunneling spectroscopy study, over a broad doping, temperature, and bias range, in epitaxial $c$-axis $\mathrm{L}{\mathrm{a}}_{2\ensuremath{-}x}\mathrm{S}{\mathrm{r}}_{x}\mathrm{Cu}{\mathrm{O}}_{4}/\mathrm{L}{\mathrm{a}}_{2}\mathrm{Cu}{\mathrm{O}}_{4}/\mathrm{L}{\mathrm{a}}_{2\ensuremath{-}x}\mathrm{S}{\mathrm{r}}_{x}\mathrm{Cu}{\mathrm{O}}_{4}$ heterostructures. The behavior of these superconductor/insulator/superconductor (SIS) devices is unusual. Down to 20 mK there is complete suppression of $c$-axis Josephson critical current with a barrier of only 2 nm of $\mathrm{L}{\mathrm{a}}_{2}\mathrm{Cu}{\mathrm{O}}_{4}$, and the zero-bias conductance remains at 20--30% of the normal-state conductance, implying a substantial population of in-gap states. Tunneling spectra show greatly suppressed coherence peaks. As the temperature is raised, the superconducting gap fills in rather than closing at ${T}_{c}$. For all doping levels, the spectra show an inelastic tunneling feature at \ensuremath{\sim}80 meV, suppressed as T exceeds ${T}_{c}$. These nominally simple epitaxial cuprate junctions deviate markedly from expectations based on the standard Bardeen-Cooper-Schrieffer theory.

5 citations

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TL;DR: In this article, phase coherent transport properties of double-gated mono-, bi-, and trilayer bilayers were investigated and the authors found that the spin relaxation time is inversely proportional to momentum relaxation time, indicating that the D'yakonov-Perel mechanism is dominant in all devices.
Abstract: Bilayer $\mathrm{Mo}{\mathrm{S}}_{2}$ is a centrosymmetric semiconductor with degenerate spin states in the six valleys at the corners of the Brillouin zone. It has been proposed that breaking of this inversion symmetry by an out-of-plane electric field breaks this degeneracy, allowing for spin and valley lifetimes to be manipulated electrically in bilayer $\mathrm{Mo}{\mathrm{S}}_{2}$ with an electric field. In this work, we report phase coherent transport properties of double-gated mono-, bi-, and trilayer $\mathrm{Mo}{\mathrm{S}}_{2}$. We observe a similar crossover from weak localization to weak antilocalization, from which we extract the spin relaxation time as a function of both electric field and temperature. We find that the spin relaxation time is inversely proportional to momentum relaxation time, indicating that the D'yakonov-Perel mechanism is dominant in all devices despite the centrosymmetry of the bilayer device. Further, we found no evidence of electric-field-induced changes in spin-orbit coupling strength. This suggests that the interlayer coupling is sufficiently weak and that electron-doped dichalcogenide multilayers behave electrically as decoupled monolayers.

4 citations

DOI
TL;DR: In this article , the electrical transport of a two-dimensional non-Fermi liquid with disorder was studied, and both the semiclassical dc conductivity and the first quantum correction were derived.
Abstract: We study the electrical transport of a two-dimensional non-Fermi liquid with disorder, and we determine both the semiclassical dc conductivity and the first quantum correction. We consider a system with N flavors of fermions coupled to SU( N ) critical matrix bosons. Motivated by the SYK model, we employ the bilocal field formalism and derive a set of finite-temperature saddle-point equations governing the fermionic and bosonic self-energies in the large- N limit. Interestingly, disorder smearing induces marginal Fermi liquid (MFL) behavior. Consequently, the resistivity varies linearly with temperature on top of the Drude result. We also consider fluctuations around the saddle points and derive a MFL-Finkel’stein nonlinear sigma model. We find that the Altshuler-Aronov quantum conductance correction also gives linear- T resistivity, and in fact dominates at low temperatures. The strong temperature dependence of the quantum correction arises due to rapid relaxation of the mediating quantum-critical bosons. We verify that our calculations explicitly satisfy the Ward identity at the semiclassical and quantum levels. Our results establish that quantum interference persists in 2-particle hydrodynamic modes, even when quasiparticles are subject to strong (Planckian) dissipation.

4 citations


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[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

Journal ArticleDOI
TL;DR: In this article, the authors measured the resistivity, specific heat and magnetoresistance of UTe2 and found that the specific heat shows a large jump at Tsc indicating strong coupling.
Abstract: We grew single crystals of the recently discovered heavy fermion superconductor UTe2, and measured the resistivity, specific heat and magnetoresistance. Superconductivity (SC) was clearly detected at Tsc=1.65K as sharp drop of the resistivity in a high quality sample of RRR=35. The specific heat shows a large jump at Tsc indicating strong coupling. The large Sommerfeld coefficient, 117mJ K-2mol-1 extrapolated in the normal state and the temperature dependence of C/T below Tsc are the signature of unconventional SC. The discrepancy in the entropy balance at Tsc between SC and normal states points out that hidden features must occur. Surprisingly, a large residual value of the Sommerfeld coefficient seems quite robust (gamma_0/gamma ~ 0.5). The large upper critical field Hc2 along the three principal axes favors spin-triplet SC. For H // b-axis, our experiments do not reproduce the huge upturn of Hc2 reported previously. This discrepancy may reflect that Hc2 is very sensitive to the sample quality. A new perspective in UTe2 is the proximity of a Kondo semiconducting phase predicted by the LDA band structure calculations.

85 citations

Journal Article
TL;DR: In this article, a magnetic field dependent non-local DC voltage and sharp resonances in the transmission of electromagnetic waves at frequencies controlled by the magnetic field are investigated for Fermi arcs.
Abstract: Surface Fermi arcs are the most prominent manifestation of the topological nature of Weyl semimetals. In the presence of a static magnetic field oriented perpendicular to the sample surface, their existence leads to unique inter-surface cyclotron orbits. We propose two experiments which directly probe the Fermi arcs: a magnetic field dependent non-local DC voltage and sharp resonances in the transmission of electromagnetic waves at frequencies controlled by the field. We show that these experiments do not rely on quantum mechanical phase coherence, which renders them far more robust and experimentally accessible than quantum effects. We also comment on the applicability of these ideas to Dirac semimetals.

44 citations

Journal ArticleDOI
10 Jul 2020-ACS Nano
TL;DR: This work highlights that the effect of dopant is not only confined in the in-plane electrical transport behavior, but also could be used to activate out-of-plane interaction between adjacent layers to tailor the electrical transport of the bilayer transitional metal dichalcogenides, which may bring different applications in electronic and optoelectronic devices.
Abstract: Interlayer interaction could substantially affect the electrical transport in transition metal dichalcogenides, serving as an effective way to control the device performance. However, it is still challenging to utilize interlayer interaction in weakly interlayer-coupled materials such as pristine MoS2 to realize layer-dependent tunable transport behavior. Here, we demonstrate that, by substitutional doping of vanadium atoms in the Mo sites of the MoS2 lattice, the vanadium-doped monolayer MoS2 device exhibits an ambipolar field effect characteristic, while its bilayer device demonstrates a heavy p-type field effect feature, in sharp contrast to the pristine monolayer and bilayer MoS2 devices, both of which show similar n-type electrical transport behaviors. Moreover, the electrical conductance of the doped bilayer MoS2 device is drastically enhanced with respect to that of the doped monolayer MoS2 device. Employing first-principle calculations, we reveal that such striking behaviors arise from the presence of electrical transport networks associated with the enhanced interlayer hybridization of S-3pz orbitals between adjacent layers activated by vanadium dopants in the bilayer MoS2, which is nevertheless absent in its monolayer counterpart. Our work highlights that the effect of dopant not only is confined in the in-plane electrical transport behavior but also could be used to activate out-of-plane interaction between adjacent layers in tailoring the electrical transport of the bilayer transitional metal dichalcogenides, which may bring different applications in electronic and optoelectronic devices.

34 citations