arXiv subjects

Jared Dans

Publications and source records attributed to Jared Dans.

3 recordsLinked to original sources

arXiv2026

Quantum oscillations and Dirac dispersion in tunable kagome lattice Lu$_{1-y}$Y$_y$(Nb$_{1-x}$Ta$_x$)$_6$Sn$_6$

Kagome lattice crystal systems present interesting symmetry-protected band structure features such as flat bands, van Hove singularities, and linearly dispersing Dirac/Weyl points that provide a rich playground for strongly correlated electron physics. Motivated by the rich properties and charge density wave evolution through the 1-6-6 series of compounds, we present our results in single crystal growth and characterization of the of Lu$_{1-y}$Y$_y$(Nb$_{1-x}$Ta$_x$)$_6$Sn$_6$ double-alloy system, including evolution of the charge density wave transition, electrical transport behavior and resultant phase diagrams. Using a novel growth technique, the synthesis of high quality crystals with extended length along the crystallographic $c$-axis allows us to follow the gradual suppression of charge density wave (CDW) order with Y substitution, and observe quantum oscillations in both magnetoresistance and magnetization throughout the series. We review the evolution of Fermi surfaces, effective masses and quasiparticle dispersion through the alloy series, revealing a decrease in size of Fermi surfaces that trends with both substitutions, and a scaling between effective mass and Fermi wavevector that suggests a regime with Dirac-like dispersion. The ability to fine-tune crystallographic, ground state and electronic dispersion properties of the \lit\ system with minimal impact of disorder opens a path torward further understanding the nature of the kagome lattice and its novel states and interactions.

cond-mat.str-el↗

arXiv2026

Thermodynamic Discovery of Tetracriticality and Emergent Multicomponent Superconductivity in UTe$_2$

The candidate topological superconductor UTe$_2$ exhibits a complex phase diagram with multiple superconducting states, yet the nature of their coexistence has remained a central mystery. In particular, the apparent intersection of two second-order phase boundaries at a ``triple point'' in the pressure-temperature phase diagram is thermodynamically forbidden, suggesting either hidden phase transitions or a fundamental misunderstanding of the superconductivity in UTe$_2$. Here, we use pulse-echo ultrasound to resolve this puzzle by discovering a new phase boundary that is characterized by a unique ``upward jump" in the sound velocity -- direct thermodynamic evidence for a phase transition where superconducting order is lost upon cooling. Our results establish $\left(P^{\star},T^{\star}\right)$ as a tetracritical point, beyond which the ambient and pressure-induced superconducting order parameters form a multi-component state. We use the measured phase diagram to demonstrate that strong competition between the two superconducting order parameters drives the loss of order on cooling, and leads to phase locking that suppresses superconducting fluctuations. These findings provide the definitive magnetic field-temperature-pressure phase diagram of UTe$_2$, and establish a thermodynamic foundation for multi-component -- and potentially topological -- superconductivity.

cond-mat.supr-con↗

arXiv2026

Vanishing Phase Stiffness and Fluctuation-Dominated Superconductivity: Evidence for Inter-Band Pairing in UTe$_2$

Superconductivity in three dimensions is almost universally governed by Ginzburg-Landau mean field theory, with critical fluctuations typically confined to within a few percent of the transition temperature ($T_{\rm c}$). We report that the heavy-Fermion superconductor UTe$_2$ exhibits a fluctuation regime that extends over a temperature range as wide as $T_{\rm c}$ itself -- the largest observed for any three-dimensional superconductor. Through ultrasound measurements of the elastic moduli and sound attenuation, we find that UTe$_2$ transitions from a mean-field-like state at ambient pressure to a fluctuation dominated state at higher pressures. This regime is marked by elastic softening and an increase in sound attenuation that onsets well above $T_{\rm c}$, with the attenuation remaining anomalously high deep in the superconducting state. Our analysis shows that these features stem from an extremely low superfluid phase stiffness. This results in a kinetic inductance as high as that of granular aluminum, but achieved in the clean limit. We propose that this exotic state is driven by dominant inter-band pairing mediated by ferromagnetic fluctuations, leading to "local" cooper pairs with a coherence length of only a few lattice constants.

cond-mat.supr-con↗