comparison-two-different-synthesis-methods-single-crystals

Comparison of Two Different Synthesis Methods of Single Crystals of Superconducting Uranium Ditelluride

Single crystal specimens of the actinide compound uranium ditelluride, UTe2, are of great importance to the study and characterization of its dramatic ...

University of Maryland

National Institute of Standards and Technology

We report superconductivity and magnetism in a new family of topological semimetals, the ternary half-Heusler compound RPdBi (R: rare earth). In this series, tuning of the rare earth f-electron component allows for simultaneous control of both lattice density via lanthanide contraction and the strength of magnetic interaction via de Gennes scaling, allowing for a unique tuning of the normal-state band inversion strength, superconducting pairing, and magnetically ordered ground states. Antiferromagnetism with ordering vector (½,½,½) occurs below a Néel temperature that scales with de Gennes factor dG, whereas a superconducting transition is simultaneously supressed with increasing dG. With superconductivity appearing in a system with noncentrosymmetric crystallographic symmetry, the possibility of spin-triplet Cooper pairing with nontrivial topology analogous to that predicted for the normal-state electronic structure provides a unique and rich opportunity to realize both predicted and new exotic excitations in topological materials. 

Topological RPdBi half-Heusler semimetals: A new family of noncentrosymmetric magnetic superconductors.

Spin-triplet superconductors potentially host topological excitations that are of interest for quantum information processing. We report the discovery of spin-triplet superconductivity in UTe, featuring a transition temperature of 1.6 kelvin and a very large and anisotropic upper critical field exceeding 40 teslas. This superconducting phase stability suggests that UTe is related to ferromagnetic superconductors such as UGe, URhGe, and UCoGe. However, the lack of magnetic order and the observation of quantum critical scaling place UTe at the paramagnetic end of this ferromagnetic superconductor series. A large intrinsic zero-temperature reservoir of ungapped fermions indicates a highly unconventional type of superconducting pairing.

Nearly ferromagnetic spin-triplet superconductivity.

Novel electronic phenomena frequently form in heavy-fermions because of the mutual localized and itinerant nature of -electrons. On the magnetically ordered side of the heavy-fermion phase diagram, -moments are expected to be localized and decoupled from the Fermi surface. It remains ambiguous whether Kondo lattice can develop inside the magnetically ordered phase. Using spectroscopic imaging with scanning tunneling microscope, complemented by neutron scattering, x-ray absorption spectroscopy, and dynamical mean field theory, we probe the electronic states in antiferromagnetic USb. We visualize a large gap in the antiferromagnetic phase within which Kondo hybridization develops below ~80 K. Our calculations indicate the antiferromagnetism and Kondo lattice to reside predominantly on different -orbitals, promoting orbital selectivity as a new conception into how these phenomena coexist in heavy-fermions. Finally, at 45 K, we find a novel first order-like transition through abrupt emergence of nontrivial 5-electronic states that may resemble the "hidden-order" phase of URuSi.

Orbital-selective Kondo lattice and enigmatic  electrons emerging from inside the antiferromagnetic phase of a heavy fermion.

Applied magnetic fields underlie exotic quantum states, such as the fractional quantum Hall effect and Bose-Einstein condensation of spin excitations. Superconductivity, however, is inherently antagonistic towards magnetic fields. Only in rare cases can these effects be mitigated over limited fields, leading to re-entrant superconductivity. Here, we report the coexistence of multiple high-field re-entrant superconducting phases in the spin-triplet superconductor UTe (ref. ). We observe superconductivity in the highest magnetic field range identified for any re-entrant superconductor, beyond 65 T. Although the stability of superconductivity in these high magnetic fields challenges current theoretical models, these extreme properties seem to reflect a new kind of exotic superconductivity rooted in magnetic fluctuations and boosted by a quantum dimensional crossover.

Extreme magnetic field-boosted superconductivity.

Spin triplet superconductivity in the Kondo lattice UTe appears to be associated with spin fluctuations originating from incipient ferromagnetic order. Here we show clear evidence of twofold enhancement of superconductivity under pressure, which discontinuously transitions to magnetic order, likely of ferromagnetic nature, at higher pressures. The application of a magnetic field tunes the system back across a first-order phase boundary. Straddling this phase boundary, we find another example of reentrant superconductivity in UTe. As the superconductivity and magnetism exist on two opposite sides of the first-order phase boundary, our results indicate other microscopic mechanisms may be playing a role in stabilizing spin triplet superconductivity in addition to spin fluctuations associated with magnetism.

Article	Year
Topological RPdBi half-Heusler semimetals: A new family of noncentrosymmetric magnetic superconductors. Science advances\| PubMed ID: 26601201	2015
Nearly ferromagnetic spin-triplet superconductivity. Science (New York, N.Y.)\| PubMed ID: 31416960	2019
Orbital-selective Kondo lattice and enigmatic electrons emerging from inside the antiferromagnetic phase of a heavy fermion. Science advances\| PubMed ID: 31667341	2019
Extreme magnetic field-boosted superconductivity. Nature physics\| PubMed ID: 34131432	2019
Enhancement and reentrance of spin triplet superconductivity in UTe under pressure. Physical review. B\| PubMed ID: 34131608	2020

Shanta R. Saha

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