Unconventional Superconductivity in UTe2

Abstract

The novel spin-triplet superconductor candidate UTe2 was discovered only recently at the end of 2018 and attracted enormous attention. We review key experimental and theoretical progress which has been achieved in different laboratories. UTe2 is a heavy-fermion paramagnet, but right after 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. The competition between different types of magnetic interactions and the duality between the local and itinerant character of the 5f Uranium 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. Special attention will be given to the occurrence of a metamagnetic transition at Hm = 35 T for a magnetic field applied along the hard magnetic axis b. Adding external pressure leads to strong changes in the magnetic and electronic properties with a direct feedback on superconductivity. Attention will be given on the possible evolution of the Fermi surface as a function of magnetic field and pressure. Superconductivity in UTe2 is 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 diagram. There is evidence for spin-triplet pairing. The different theoretical approaches will be described. Notably we discuss that UTe2 is a possible example for the realization of a fascinating topological superconductor.

47 pages, 53 figures, submitted to J. Phys.: Condens. Matter as "Topical Review"

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Cited by in corpus (116)

• Flat bands, strange metals, and the Kondo effect
• Detection of a Pair Density Wave State in UTe${}_2$
• Single-component superconducting state in UTe2 at 2 K
• First Observation of de Haas-van Alphen Effect and Fermi Surfaces in Unconventional Superconductor UTe2
• Superconductivity and Local Inversion-Symmetry Breaking
• Magnetic-field sensitive charge density wave orders in the superconducting phase of UTe2
• Large Reduction in the $a$-axis Knight Shift on UTe${}_2$ with $T_{\mathrm{c}}$ = 2.1 K
• Field-induced tuning of the pairing state in a superconductor
• Quasi-2D Fermi surface in the anomalous superconductor UTe2
• A review of UTe${}_2$ at high magnetic fields
• The fate of time-reversal symmetry breaking in UTe2
• Fully gapped pairing state in spin-triplet superconductor UTe${}_2$
• Change of superconducting character in UTe2induced by magnetic field
• Even-odd parity transition in strongly correlated locally noncentrosymmetric superconductors : An application to CeRh${}_2$As${}_2$
• Triplet pairing mechanisms from Hund's-Kondo models: applications to UTe${}_2$ and CeRh${}_2$As${}_2$
• Enhanced triplet superconductivity in next generation ultraclean UTe2
• Quantum-geometry-induced anapole superconductivity
• Quantum interference between quasi-2D Fermi surface sheets in UTe2
• Microscopic imaging homogeneous and single phase superfluid density in UTe${}_2$
• Heat capacity double transitions in time-reversal symmetry broken superconductors
• Spin-triplet superconductivity from quantum-geometry-induced ferromagnetic fluctuation
• Field-induced compensation of magnetic exchange as the possible origin of reentrant superconductivity in UTe${}_2$
• de Haas-van Alphen Oscillations for the Field Along c-axis in UTe2
• Thermodynamic and electrical transport properties of UTe${}_2$ under uniaxial stress
• Longitudinal spin fluctuations driving field-reinforced superconductivity in UTe${}_2$
• Pressure-induced structural phase transition and new superconducting phase in UTe2
• Molten Salt Flux Liquid Transport Method for Ultra Clean Single Crystals UTe2
• Nonreciprocal Meissner response in parity-mixed superconductors
• Chiral Superconductivity in UTe${}_2$ via Emergent $C_4$ Symmetry and Spin Orbit Coupling
• Spontaneous time-reversal symmetry breaking by disorder in superconductors
• Pairing symmetries of multiple superconducting phases in UTe2: Competition between ferromagnetic and antiferromagnetic fluctuations
• Magnetovolume Effect on the First-Order Metamagnetic Transition in UTe${}_2$
• Piezoelectric effect and diode effect in anapole and monopole superconductors
• Anomalous upper critical field in the quasicrystal superconductor Ta${}_{1.6}$Te
• Anisotropic signatures of the electronic correlations in the electrical resistivity of UTe${}_2$
• Anomalous vortex dynamics in spin-triplet superconductor UTe${}_2$
• Odd-Parity Quasiparticle Interference in the Superconductive Surface State of UTe2
• Pair Wavefunction Symmetry in UTe2 from Zero-Energy Surface State Visualization
• Superconducting Diode Effect in Multiphase Superconductors
• Multiple superconducting phases in heavy-fermion metals
• Drastic change in magnetic anisotropy of UTe2 under pressure revealed by 125Te-NMR
• Structure of the normal state and origin of Schottky anomaly in the correlated heavy fermion superconductor UTe2
• Metastable phase of UTe${}_2$ formed under high pressure above 5 GPa
• Thermodynamic transitions and topology of spin-triplet superconductivity: Application to UTe${}_2$
• Magnon Bose-Einstein condensates: from time crystals and quantum chromodynamics to vortex sensing and cosmology
• Nonreciprocal superconductivity
• Inhomogeneous high temperature melting and decoupling of charge density waves in spin-triplet superconductor UTe2
• c axis electrical transport at the metamagnetic transition in the heavy-fermion superconductor UTe2 under pressure
• Anisotropic Enhancement of Lower Critical Field in Ultraclean Crystals of Spin-Triplet Superconductor UTe2
• Clear Reduction in Spin Susceptibility and Superconducting Spin Rotation for $H\parallel a$ in the Early-Stage Sample of Spin-Triplet Superconductor UTe${}_2$
• Theory of the low- and high-field superconducting phases of UTe${}_2$
• A quantum critical line bounds the high field metamagnetic transition surface in UTe${}_2$
• Magnetic parity violation and parity-time-reversal-symmetric magnets
• Intrinsic Anomalous Thermal Hall Effect in the Unconventional Superconductor UTe2
• Incommensurate antiferromagnetism in UTe2 under pressure
• Anisotropic field-induced changes in the superconducting order parameter of UTe2
• Observation of odd-parity superconductivity in UTe2
• Reinforcement of superconductivity by quantum critical fluctuations of metamagnetism in UTe${}_2$
• Floquet engineering triplet superconductivity in superconductors with spin-orbit coupling or altermagnetism
• Violation of the orbital depairing limit in a non-unitary state --on the high field phase in the heavy Fermion superconductor UTe${}_2$--
• Time-reversal symmetry breaking from lattice dislocations in superconductors
• Anisotropic paramagnetic response of topological Majorana surface states in the superconductor ${\text{UTe}}_2$
• Unconventional $s$-Wave Pairing with Point-Node-Like Gap Structure in UTe${}_2$
• Intrinsic low-temperature magnetic properties on the ultra-clean UTe${}_2$ with $T_{\mathrm{c}}$ = 2.1 K revealed by ${}^{125}$Te NMR
• Observation of Persistent Zero Modes and Superconducting Vortex Doublets in UTe${}_2$
• Hydrostatic pressure studies on non-superconducting UTe2
• Theoretical studies on off-axis phase diagrams and Knight shifts in UTe${}_2$ -- Tetra-critical point, d-vector rotation, and multiple phases
• Topological Kondo effect with spinful Majorana fermions
• Spectroscopic evidence of symmetry breaking in the superconducting vortices of UTe2
• Nodal superconducting gap structure and topological surface states of UTe${}_2$
• Spin caloritronics as a probe of nonunitary superconductors
• Pair-Kondo effect: a mechanism for time-reversal broken superconductivity in UTe${}_2$
• Superconducting meron phase in locally noncentrosymmetric superconductors
• Competition of vortex core structures in superfluid ${}^3$He-B
• Dramatic elastic response at the critical end point in UTe${}_2$
• Self-reconstruction of order parameter in spin-triplet superconductor UTe${}_2$
• Microscopic theory of pair density waves in spin-orbit coupled Kondo lattice
• Majorana multipole response with magnetic point group symmetry
• Thermal conductivity of nonunitary triplet superconductors: application to UTe${}_2$
• Anomalous Field-Temperature Phase Diagram of Superconductivity in Sn-Pb Solder
• Magnetic signatures of pressure-induced multicomponent superconductivity in UTe${}_2$
• Two-dimensional flat band on the (011) surface of UTe${}_2$: Implication for STM measurements with a superconducting tip
• Reciprocal and nonreciprocal paraconductivity in bilayer multiphase superconductors
• Topological superconductivity in a spin-orbit coupled Kondo lattice
• Observation of vortex stripes in UTe${}_2$
• Emergent ferromagnetic ladder excitations in heavy fermion superconductor CeSb${}_2$
• Higher-order topological phases for time-reversal-symmetry breaking superconductivity in UTe${}_2$
• $b$-axis and $c$-axis Knight shift measurements in the superconducting state on ultraclean UTe${}_2$ with $T_c$ = 2.1 K
• Structure-Driven Prediction of Magnetic Order in Uranium Compounds
• Metamagnetism in the high-pressure tetragonal phase of UTe${}_2$
• Finite-momentum and field-induced pairings in orbital-singlet spin-triplet superconductors
• Slow magnetic quantum oscillations in the c-axis magnetoresistance of UTe${}_2$
• Spin susceptibility of nonunitary spin-triplet superconductors
• Theory of the Little-Parks effect in spin-triplet superconductors
• Optical and Raman selection rules for odd-parity clean superconductors
• Magnetic edge fields in UTe${}_2$ near zero background fields
• Particle-hole spectral asymmetry at the edge of multiorbital noncentrosymmetric superconductors
• Nature of quantum criticality in the Ising ferromagnet TbV${}_6$Sn${}_6$
• A unified theoretical framework for Kondo superconductors: Periodic Anderson impurities with attractive pairing and Rashba spin-orbit coupling
• Antiferromagnetic Order and Magnetic Frustration in the Honeycomb Heavy-Fermion System Ce(Pt${}_{1-x}$Pd${}_x$)${}_6$Al${}_3$: ${}^{27}$Al and ${}^{195}$Pt NMR Studies
• Visualizing the Odd-parity Superconducting Order Parameter and its Quasiparticle Surface Band in UTe2
• Nuclear spin relaxation rate of nonunitary Dirac and Weyl superconductors
• Nodal Superconductivity of UTe${}_2$ Probed by Field-Angle-Resolved Specific Heat on a Crystal with $T_{\mathrm{c}}=2.1$ K
• Magnetic fluctuations and anisotropy in UTe2: a multi-orbital study based on GGA+U and RPA
• Metamagnetism and tricriticalilty in heavy-fermion ferromagnet URhGe
• Pressure-enhanced $f$-electron orbital weighting in UTe2 mapped by quantum interferometry
• Unconventional superconductivity emerging along with the strange-metal behavior in UAs2 under pressure
• Theoretical Study of Impurity Effects on Superconductivity in UTe2
• Spin-triplet pairing instability in a two-dimensional repulsive Hubbard model
• Quantum geometric magnetic monopole and two-phase superconductivity in CeRh${}_2$As${}_2$
• Raman response of collective modes in multicomponent superconductors
• Scanning Tunneling Microscopy in high vectorial magnetic fields
• Topological superconductivity in helical crystals
• Electronic structure of UTe${}_2$ under pressure
• Quasiparticle Interference of Spin-Triplet Superconductors: Application to UTe${}_2$
• Designing edge currents using mesoscopic patterning in chiral d-wave superconductors