arXiv subjects

Benjamin Gregory

Publications and source records attributed to Benjamin Gregory.

4 recordsLinked to original sources

arXiv2026

Anisotropic Superconductivity with Enhanced Critical Field in Strained RuO2

The superconductivity in RuO2 emerges under strain. RuO2 is also an altermagnet candidate. The nature of superconductivity and its relation with neighboring orders, however, are not understood. To address this problem, we grew epitaxial RuO2 films on TiO2(100) and TiO2(110) single crystal substrates and studied the electronic transport and emergent superconductivity along various crystallographic directions. We show that the superconducting transition strongly depends on the growth orientation and the crystallographic direction of the transport in the RuO2 films. We also observe a strong violation of Pauli paramagnetic limit with in-plane applied magnetic field which we attribute to strong spin-orbit scattering. These results offer opportunities for epitaxially engineered superconductors.

cond-mat.supr-con↗

arXiv2026

Martensitic laminate geometry controls electronic phase transitions in a Mott insulator

Symmetry-lowering structural phase transitions result in multiple degenerate structures whose coexistence is determined by macroscopic strain compatibility. In quantum materials, these structural transformations often couple to electronic degrees of freedom, yet how the structural arrangements influence electronic phase transitions remains poorly understood. By analyzing hundreds of diffraction peaks from X-ray reciprocal space mapping, we determine the lattice basis vectors and mutual orientations of all coexisting phases in epitaxial V2O3 thin films after a symmetry-lowering transformation coincident with a metal-insulator transition. We identify the orientations of interfaces between all coexisting structures using the theory of martensitic phase transformations and find that the low temperature structure comprises finely tuned layered mixtures of alternating twin variants, akin to metal alloys. By comparing films grown on various substrate orientations, we show that the metal-insulator transition temperature increases monotonically with the degree to which these layered mixtures satisfy macroscopic strain compatibility imposed by the substrate.

cond-mat.mtrl-sci↗

arXiv2022

Strain-induced orbital energy shift in antiferromagnetic RuO2 revealed by resonant elastic x-ray scattering

In its ground state, RuO2 was long thought to be an ordinary metallic paramagnet. Recent neutron and x-ray diffraction revealed that bulk RuO2 is an antiferromagnet (AFM) with TN above 300 K. Furthermore, epitaxial strain induces novel superconductivity in thin films of RuO2 below 2 K. Here, we present a resonant elastic x-ray scattering (REXS) study at the Ru L2 edge of the strained RuO2 films exhibiting the strain-induced superconductivity. We observe an azimuthal modulation of the 100 Bragg peak consistent with canted AFM found in bulk. Most notably, in the strained films displaying novel superconductivity, we observe a ~1 eV shift of the Ru eg orbitals to a higher energy. The energy shift is smaller in thicker, relaxed films and films with a different strain direction. Our results provide further evidence of the utility of epitaxial strain as a tuning parameter in complex oxides.

cond-mat.str-el↗

arXiv2020

Phonon-assisted formation of an itinerant electronic density wave

Electronic instabilities drive ordering transitions in condensed matter. Despite many advances in the microscopic understanding of the ordered states, a more nuanced and profound question often remains unanswered: how do the collective excitations influence the electronic order formation? Here, we experimentally show that a phonon affects the spin density wave (SDW) formation after an SDW-quench by femtosecond laser pulses. In a thin film, the temperature-dependent SDW period is quantized, allowing us to track the out-of-equilibrium formation path of the SDW precisely. By exploiting its persistent coupling to the lattice, we probe the SDW through the transient lattice distortion, measured by femtosecond X-ray diffraction. We find that within 500 femtoseconds after a complete quench, the SDW forms with the low-temperature period, directly bypassing a thermal state with the high-temperature period. We argue that a momentum-matched phonon launched by the quench changes the formation path of the SDW through the dynamic pinning of the order parameter.

cond-mat.str-el↗