182 research outputs found
Quantum Oscillations in CuBiSe in High Magnetic Fields
CuBiSe has drawn much attention as the leading candidate to be
the first topological superconductor and the realization of coveted Majorana
particles in a condensed matter system. However, there has been increasing
controversy about the nature of its superconducting phase. This study sheds
light on present ambiguity in the normal state electronic state, by providing a
complete look at the quantum oscillations in magnetization in
CuBiSe at intense high fields up to 31T. Our study focuses on the
angular dependence of the quantum oscillation pattern in a low carrier
concentration. As magnetic field tilts from along the crystalline c-axis to
ab-plane, the change of the oscillation period follows the prediction of the
ellipsoidal Fermi surface. As the doping level changes, the 3D Fermi surface is
found to transform into quasi-cylindrical at high carrier density. Such a
transition is potentially a Lifshitz transition of the electronic state in
CuBiSe.Comment: 6 pages, 6 figures, submitted to Phys. Rev.
Probing quantum criticality in ferromagnetic CeRh6Ge4
CeRhGe is unusual in that its ferromagnetic transition can be
suppressed continuously to zero temperature, i.e., to a ferromagnetic
quantum-critical point (QCP), through the application of modest hydrostatic
pressure. This discovery has raised the possibility that the ferromagnetic QCP
may be of the Kondo-breakdown type characterized by a jump in Fermi volume, to
which thermopower S measurements should be sensitive. Though changes both
sign and magnitude around the critical pressure P GPa, these
changes are not abrupt but extend over a pressure interval from within the
ferromagnetic state up to P. Together with temperature and pressure
variations in electrical resistivity and previously reported heat capacity,
thermopower results point to the near coincidence of two sequential effects
near P, delocalization of 4f degrees-of-freedom through orbital-selective
hybridization followed by quantum criticality of itinerant ferromagnetism.Comment: 6 pages, 3 figure
The magnetic phase diagram of underdoped YBa2Cu3Oy inferred from torque magnetization and thermal conductivity
Strong evidence for charge-density correlation in the underdoped phase of the
cuprate YBa2Cu3Oy was obtained by nuclear magnetic resonance (NMR) and resonant
x-ray scatter- ing. The fluctuations were found to be enhanced in strong
magnetic fields. Recently, 3D (three dimensional) charge-density wave (CDW)
formation with long-range order (LRO) was observed by x-ray diffraction in H
>15 T. To elucidate how the CDW transition impacts the pair condensate, we have
used torque magnetization to 45 T and thermal conductivity to
construct the magnetic phase diagram in untwinned crystals with hole density p
= 0.11. We show that the 3D CDW transitions appear as sharp features in the
susceptibility and at the fields HK and Hp, which define phase
boundaries in agreement with spectroscopic techniques. From measurements of the
melting field Hm(T) of the vortex solid, we obtain evidence for two vortex
solid states below 8 K. At 0.5 K, the pair condensate appears to adjust to the
3D CDW by a sharp transition at 24 T between two vortex solids with very
different shear moduli. At even higher H (42 T) the second vortex solid melts
to a vortex liquid which survives to fields well above 45 T. de Haas-van Alphen
oscillations appear at fields 24-28 T, below the lower bound for the upper
critical field Hc2.Comment: 7 pages, 8 figures; New version of previous posting, reporting torque
measurements to 45 Tesla and final magnetic phase diagra
Exotic heavy-fermion superconductivity in atomically thin CeCoIn5 films
Funding: This work is supported by Grants-in-Aid for Scientific Research (KAKENHI) (Grants No. JP18H01180, No. JP18H05227, and No. JP18K03511) from Japan Society for the Promotion of Science (JSPS), and by Core Research for Evolutional Science and Technology (CREST) (Grant No. JP-MJCR19T5) from Japan Science and Technology Agency (JST).We report an in situ scanning tunneling microscopy study of atomically thin films of CeCoIn5, a d-wave heavy-fermion superconductor. Both hybridization and superconducting gaps are observed even in monolayer CeCoIn5, providing direct evidence of superconductivity of heavy quasiparticles mediated by purely two-dimensional bosonic excitations. In these atomically thin films, Tc is suppressed to nearly half of the bulk, but is similar to CeCoIn5/YbCoIn5 superlattices containing CeCoIn5 layers with the same thickness as the thin films. Remarkably, the out-of-plane upper critical field μ0Hc2⊥ at zero temperature is largely enhanced from those of bulk and superlattices. The enhanced Hc2⊥ well exceeds the Pauli and bulk orbital limits, suggesting the possible emergence of unusual superconductivity with parity mixing caused by the inversion symmetry breaking.Publisher PDFPeer reviewe
Quantum oscillations in Kondo Insulator SmB
In Kondo insulator samarium hexaboride SmB, strong correlation and band
hybridization lead to an insulating gap and a diverging resistance at low
temperature. The resistance divergence ends at about 5 Kelvin, a behavior
recently demonstrated to arise from the surface conductance. However, questions
remain whether and where a topological surface state exists. Quantum
oscillations have not been observed to map the Fermi surface. We solve the
problem by resolving the Landau Level quantization and Fermi surface topology
using torque magnetometry. The observed Fermi surface suggests a two
dimensional surface state on the (101) plane. Furthermore, the tracking of the
Landau Levels in the infinite magnetic field limit points to -1/2, which
indicates a 2D Dirac electronic state
- …