Field-induced transition within the superconducting state of CeRh2As2
27 Aug 2021-Science (American Association for the Advancement of Science)-Vol. 373, Iss: 6558, pp 1012-1016
TL;DR: In this article, the authors reported the discovery of two-phase unconventional superconductivity in CeRh2As2 using thermodynamic probes, and established that the superconducting critical field of its high-field phase is as high as 14 tesla, even though the transition temperature is only 0.26 kelvin.
Abstract: Materials with multiple superconducting phases are rare. Here, we report the discovery of two-phase unconventional superconductivity in CeRh2As2 Using thermodynamic probes, we establish that the superconducting critical field of its high-field phase is as high as 14 tesla, even though the transition temperature is only 0.26 kelvin. Furthermore, a transition between two different superconducting phases is observed in a c axis magnetic field. Local inversion-symmetry breaking at the cerium sites enables Rashba spin-orbit coupling alternating between the cerium sublayers. The staggered Rashba coupling introduces a layer degree of freedom to which the field-induced transition and high critical field seen in experiment are likely related.
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TL;DR: The spin-triplet superconductor candidate UTe2 was discovered only recently at the end of 2018 and already attracted enormous attention as mentioned in this paper , showing an exceptionally huge superconducting upper critical field with a reentrant behavior under magnetic field and the occurrence of multiple super-conducting phases in the temperature-field-pressure phase diagrams.
Abstract: The novel spin-triplet superconductor candidate UTe2was discovered only recently at the end of 2018 and already attracted enormous attention. We review key experimental and theoretical progress which has been achieved in different laboratories. UTe2is a heavy-fermion paramagnet, but following the discovery of superconductivity, it has been expected to be close to a ferromagnetic instability, showing many similarities to the U-based ferromagnetic superconductors, URhGe and UCoGe. This view might be too simplistic. The competition between different types of magnetic interactions and the duality between the local and itinerant character of the 5fUranium electrons, as well as the shift of the U valence appear as key parameters in the rich phase diagrams discovered recently under extreme conditions like low temperature, high magnetic field, and pressure. We discuss macroscopic and microscopic experiments at low temperature to clarify the normal phase properties at ambient pressure for field applied along the three axis of this orthorhombic structure. Special attention will be given to the occurrence of a metamagnetic transition atHm= 35 T for a magnetic field applied along the hard magnetic axisb. Adding external pressure leads to strong changes in the magnetic and electronic properties with a direct feedback on superconductivity. Attention is paid on the possible evolution of the Fermi surface as a function of magnetic field and pressure. Superconductivity in UTe2is extremely rich, exhibiting various unconventional behaviors which will be highlighted. It shows an exceptionally huge superconducting upper critical field with a re-entrant behavior under magnetic field and the occurrence of multiple superconducting phases in the temperature-field-pressure phase diagrams. There is evidence for spin-triplet pairing. Experimental indications exist for chiral superconductivity and spontaneous time reversal symmetry breaking in the superconducting state. Different theoretical approaches will be described. Notably we discuss that UTe2is a possible example for the realization of a fascinating topological superconductor. Exploring superconductivity in UTe2reemphasizes that U-based heavy fermion compounds give unique examples to study and understand the strong interplay between the normal and superconducting properties in strongly correlated electron systems.
42 citations
23 Sep 2021
TL;DR: In this article, it was shown that the high-field superconducting phase of CeRh${}_{2}$As${}_1}$ is a topological crystalline superconductor, by combining the Fermi surface formula and first principle calculations.
Abstract: The authors show, by combining the Fermi-surface formula and the first principle calculations, that the high-field superconducting phase of CeRh${}_{2}$As${}_{2}$ is a topological crystalline superconductor.
22 citations
TL;DR: A review of spin-orbit coupling in non-centrosymmetric heterostructures can be found in this paper , which highlights the latest progress covering new classes of materials with a variety of Rashba-like spin-momentum locking schemes.
Abstract: Spin–orbit coupling induces a unique form of Zeeman interaction in momentum space in materials that lack inversion symmetry: the electron’s spin is locked on an effective magnetic field that is odd in momentum. The resulting interconnection between the electron’s momentum and its spin leads to various effects such as electric dipole spin resonance, anisotropic spin relaxation and the Aharonov–Casher effect, but also to electrically driven and optically driven spin galvanic effects. Over the past 15 years, the emergence of topological materials has widened this research field by introducing complex forms of spin textures and orbital hybridization. The vast field of Rashba-like physics is now blooming, with great attention paid to non-equilibrium mechanisms such as spin-to-charge conversion, but also to nonlinear transport effects. This Review aims to offer an overview of recent progress in the development of condensed matter research that exploits the unique properties of spin–orbit coupling in non-centrosymmetric heterostructures. Spin–orbit coupling in non-centrosymmetric heterostructures is called the Rashba effect. This Review highlights the latest progress covering new classes of materials with a variety of ‘Rashba-like’ spin–momentum locking schemes and new trends in non-equilibrium transport leading to enhanced functionalities in spin- and optoelectronics.
21 citations
TL;DR: In this article , the authors present evidence for antiferromagnetic order in the case of the nuclear quadrupole resonance spectrum at two crystallographically inequivalent As sites, which is a promising system to study how the absence of local inversion symmetry induces or influences unconventional magnetic and superconducting states.
Abstract: Spatial inversion symmetry in crystal structures is closely related to the superconducting (SC) and magnetic properties of materials. Recently, several theoretical proposals that predict various interesting phenomena caused by the breaking of the local inversion symmetry have been presented. However, experimental validation has not yet progressed owing to the lack of model materials. Here we present evidence for antiferromagnetic (AFM) order in CeRh_{2}As_{2} (SC transition temperature T_{SC}∼0.37 K), wherein the Ce site breaks the local inversion symmetry. The evidence is based on the observation of different extents of broadening of the nuclear quadrupole resonance spectrum at two crystallographically inequivalent As sites. This AFM ordering breaks the inversion symmetry of this system, resulting in the activation of an odd-parity magnetic multipole. Moreover, the onset of antiferromagnetism T_{N} within an SC phase, with T_{N}
18 citations
TL;DR: In this paper , it was shown that the unconventional superconductor CeRh{}_{2}$As${}_{ 2]$As{}{ 2}$ may host a quadrurupole density wave, a theorized complex ordering pattern among free electrons that has not yet been observed.
Abstract: Experiments show that the unconventional superconductor CeRh${}_{2}$As${}_{2}$ may host a ``quadrupole density wave''---a theorized complex ordering pattern among free electrons that has not yet been observed.
17 citations
References
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TL;DR: The WinGX suite provides a complete set of programs for the treatment of small-molecule single-crystal diffraction data, from data reduction and processing, structure solution, model refinement and visualization, and metric analysis of molecular geometry and crystal packing, to final report preparation in the form of a CIF.
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TL;DR: A review of renormalization group ideas in the context of critical phenomena can be found in this paper, where the authors discuss the relationship of the modern renormalisation group to the older problems of divergences in statistical mechanics and field theory.
Abstract: This review covers several topics involving renormalization group ideas. The solution of the $s$-wave Kondo Hamiltonian, describing a single magnetic impurity in a nonmagnetic metal, is explained in detail. See Secs. VII-IX. "Block spin" methods, applied to the two dimensional Ising model, are explained in Sec. VI. The first three sections give a relatively short review of basic renormalization group ideas, mainly in the context of critical phenomena. The relationship of the modern renormalization group to the older problems of divergences in statistical mechanics and field theory and field theoretic renormalization is discussed in Sec. IV. In Sec. V the special case of "marginal variables" is discussed in detail, along with the relationship of the modern renormalization group to its original formulation by Gell-Mann and Low and others.
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TL;DR: In this paper, a solution of the linearized Gor'kov equations for the upper critical magnetic field of a bulk type-II superconductor is extended to include the effects of Pauli spin paramagnetism and spin-orbit impurity scattering.
Abstract: A previously obtained solution of the linearized Gor'kov equations for the upper critical magnetic field ${H}_{c2}$ of a bulk type-II superconductor is extended to include the effects of Pauli spin paramagnetism and spin-orbit impurity scattering. To carry out the calculation, it is necessary to introduce an approximation which assumes that spin-orbit scattering is infrequent in comparison with spin-independent scattering. It is found that spin-orbit scattering counteracts the effects of the spin paramagnetism in limiting the critical field and improves agreement between theory and experiment.
2,474 citations
TL;DR: In this paper, it was shown that the depaired state has a spatially dependent complex Gorkov field, corresponding to a nonzero pairing momentum in the BCS model, and that the presence of the "normal" electrons from the broken pairs reduces the total current to zero, gives the deblating state some spin polarization, and results in almost normal Sommerfeld specific heat and single-electron tunneling characteristics.
Abstract: A strong exchange field, such as produced by ferromagnetically aligned impurities in a metal, will tend to polarize the conduction electron spins. If the metal is a superconductor, this will happen only if the spin-exchange field is sufficiently strong compared to the energy gap. When the field is strong enough to break many electron pairs, the self-consistent gap equation is modified and a new type of depaired superconducting ground state occurs. In the idealization of a spatially uniform exchange field with no scattering, it is found that the depaired state has a spatially dependent complex Gorkov field, corresponding to a nonzero pairing momentum in the BCS model. The presence of the "normal" electrons from the broken pairs reduces the total current to zero, gives the depaired state some spin polarization, and results in almost normal Sommerfeld specific heat and single-electron tunneling characteristics. The nonzero value of the pairing momentum also gives rise to an unusual anisotropic electrodynamic behavior of the superconductor, as well as to a degenerate ground state and low-lying collective excitations, in accordance with Goldstone's theorem. The effects of scattering in an actual superconducting ferromagnetic alloy have not been studied and may interfere with experimental investigation of the theoretical results found in this paper for the idealized model.
2,346 citations
TL;DR: In this paper, a review of recent developments in the phenomenological description of unconventional superconductivity is presented, starting with the BCS theory of superconductivities with anisotropic Cooper pairing, and the group-theoretical derivation of the generalized Ginzburg-Landau theory for unconventional supercondivity.
Abstract: This article is a review of recent developments in the phenomenological description of unconventional superconductivity. Starting with the BCS theory of superconductivity with anisotropic Cooper pairing, the authors explain the group-theoretical derivation of the generalized Ginzburg-Landau theory for unconventional superconductivity. This is used to classify the possible superconducting states in a system with given crystal symmetry, including strong-coupling effects and spin-orbit interaction. On the basis of the BCS theory the unusual low-temperature properties and the (resonant) impurity scattering effects are discussed for superconductors with anisotropic pairing. Using the Ginzburg-Landau theory, the authors study several bulk properties of such superconductors: spontaneous lattice distortion, upper critical magnetic field, splitting of a phase transition due to uniaxial stress. Two possible mechanisms for ultrasound absorption are discussed: collective modes and damping by domain-wall motion. The boundary conditions for the Ginzburg-Landau theory are derived from a correlation function formulation and by group-theoretical methods. They are applied to a study of the Josephson and proximity effects if unconventional superconductors are involved there. The magnetic properties of superconductors that break time-reversal symmetry are analyzed. Examples of current and magnetic-field distributions close to inhomogeneities of the superconducting order parameter are given and their physical origin is discussed. Vortices in a superconductor with a multicomponent order parameter can exhibit various topological structures. As examples the authors show fractional vortices on domain walls and nonaxial vortices in the bulk. Furthermore, the problem of the possible coexistence of a superconducting and a magnetically ordered phase in an unconventional superconductor is analyzed. The combination of two order parameters that are almost degenerate in their critical temperature is considered with respect to the phase-transition behavior and effects on the lower and upper critical fields. Because heavy-fermion superconductors---which are possible realizations of unconventional superconductivity---have been the main motivation for the phenomenological studies presented here, the authors compare the theoretical results with the experimental facts and data. In particular, they emphasize the intriguing features of the compound U${\mathrm{Pt}}_{3}$ and consider in detail the alloy ${\mathrm{U}}_{1\ensuremath{-}x}{\mathrm{Th}}_{x}{\mathrm{Be}}_{13}$.
1,577 citations