arXiv subjects

M. D. Frontzek

Publications and source records attributed to M. D. Frontzek.

6 recordsLinked to original sources

arXiv2025

Long-lived dynamics of the charge density wave in TiSe2 observed by time-resolved neutron diffraction

We use time-resolved elastic neutron scattering combined with laser heating to probe the temporal evolution of periodic lattice distortions (PLD) due to the formation of a charge density wave (CDW) state in 1T-TiSe$_{2}$ under extreme non-equilibrium conditions. Below the transition temperature, the PLD is manifested as a 2x2x2 superlattice superimposed on the average Bragg structure. Following rapid energy deposition with the laser, kinetic bottlenecks lead to a separation of timescales between the superlattice and the underlying lattice response. The superlattice melts on a characteristic timescale of approximately 3 s, whereas the average lattice responds more slowly to heating. Upon removal of the heat source, the Bragg lattice recovers within approximately 11 s, while the superlattice re-establishes on nearly twice that timescale. These results reveal an asymmetric evolution of short- and long-range order under extreme non-equilibrium conditions, in which local PLD correlations are destroyed prior to, and recover more slowly than, the average lattice structure.

cond-mat.mtrl-sci↗

arXiv2024

A Candidate for the Quantum Spin Liquid Ground-State in the Shastry-Sutherland Lattice Material Yb$_2$Be$_2$GeO$_7$

The quasi-2D Shastry-Sutherland model has remained topical in the field of condensed matter physics for the last two decades, following the experimental realization of the model in the material SrCu$_2$(BO$_3$)$_2$. Since then, research into the Shastry-Sutherland system has revealed more nuanced physics than initially predicted; recent theoretical works have even predicted a quantum spin liquid phase may exist. Herein, we report on a new Shastry-Sutherland lattice material, Yb$_2$Be$_2$GeO$_7$, of the rare-earth melilite family RE$_2$Be$_2$GeO$_7$. We find, through SQUID magnetometry, powder neutron diffraction, specific heat capacity, and muon spin relaxation, that Yb$_2$Be$_2$GeO$_7$ lacks magnetic order and exhibits persistent spin dynamics to at least 17 mK. We propose the Shastry-Sutherland lattice material Yb$_2$Be$_2$GeO$_7$ as a candidate to host a quantum spin liquid ground-state.

cond-mat.str-el↗

arXiv2024

Dipolar spin ice regime proximate to an all-in-all-out Néel ground state in the dipolar-octupolar pyrochlore Ce$_2$Sn$_2$O$_7$

The dipolar-octupolar (DO) pyrochlores, R$_2$M$_2$O$_7$ (R = Ce, Sm, Nd), are key players in the search for realizable novel quantum spin liquid (QSL) states as a large parameter space within the DO pyrochlore phase diagram is theorized to host QSL states of both dipolar and octupolar nature. New single crystals and powders of Ce$_2$Sn$_2$O$_7$, synthesized by hydrothermal techniques, present an opportunity for a new characterization of the exchange parameters in Ce$_2$Sn$_2$O$_7$ using the near-neighbor $XYZ$ model Hamiltonian associated with DO pyrochlores. Utilizing quantum numerical linked cluster expansion fits to heat capacity and magnetic susceptibility measurements, and classical Monte Carlo calculations to the diffuse neutron diffraction of the new hydrothermally grown Ce$_2$Sn$_2$O$_7$ samples, we place Ce$_2$Sn$_2$O$_7$'s ground state within the ordered dipolar all-in-all-out (AIAO) Néel phase, with quantum Monte Carlo calculations showing a transition to long-range order at temperatures below those accessed experimentally. Indeed, our new neutron diffraction measurements on the hydrothermally grown Ce$_2$Sn$_2$O$_7$ powders show a broad signal at low scattering wave vectors, reminiscent of a \textit{dipolar} spin ice, in striking contrast from previous powder neutron diffraction on samples grown from solid-state synthesis, which found diffuse scattering at high scattering wave vectors associated with magnetic {\it octupoles} and suggested an octupolar quantum spin ice state. We conclude that new hydrothermally grown Ce$_2$Sn$_2$O$_7$ samples host a finite-temperature proximate dipolar spin ice phase, above the expected transition to AIAO Néel order.

cond-mat.str-el↗

arXiv2023

Multi-k magnetic structure and large anomalous Hall effect in candidate magnetic Weyl semimetal NdAlGe

The magnetic structure, magnetoresistance, and Hall effect of non-centrosymmetric magnetic semimetal NdAlGe are investigated revealing an unusual magnetic state and anomalous transport properties that are associated with the electronic structure of this non-centrosymmetric compound. The magnetization and magnetoresistance measurements are both highly anisotropic and indicate an Ising-like magnetic system. The magnetic structure is complex in that it involves three magnetic ordering vectors including an incommensurate spin density wave and commensurate ferrimagnetic state in zero field. We have discovered a large anomalous Hall conductivity that reaches = 430 Ω-1cm-1 implying that it originates from an intrinsic Berry curvature effect stemming from Weyl nodes found in the electronic structure. These electronic structure calculations indicate the presence of nested Fermi surface pockets with nesting wave vectors similar to the measured magnetic ordering wavevector and the presence of Weyl nodes in proximity to the Fermi surface. We associate the incommensurate magnetic structure with the large anomalous Hall response to be the result of the combination of Fermi surface nesting and the Berry curvature associated with Weyl nodes.

cond-mat.mtrl-sci↗

arXiv2019

Clamp cell with $in$ $situ$ pressure monitoring for low-temperature neutron scattering measurements

A clamp pressure cell for neutron scattering experiments at low temperatures and in external magnetic fields under pressure up to 2~GPa has been fabricated and tested. The cell provides optical access to the sample space that allows instantaneous pressure determination during sample loading, cooling and measuring using ruby and/or samarium doped strontium tetraborate fluorescence monitoring. A new calibration curve of the pressure-induced shift of the $^7D_0 - ^5F_0$ (0-0) line in the fluorescent spectrum of SrB$_4$O$_7$:Sm$^{2+}$ for moderate pressures, $P\leqslant{2}$ GPa, is given.

physics.ins-det↗

arXiv2017

Evidence for a spinon Fermi surface in a triangular lattice quantum spin liquid candidate

A quantum spin liquid is an exotic quantum state of matter in which spins are highly entangled and remain disordered down to zero temperature. Such a state of matter is potentially relevant to high-temperature superconductivity and quantum-information applications, and experimental identification of a quantum spin liquid state is of fundamental importance for our understanding of quantum matter. Theoretical studies have proposed various quantum-spin-liquid ground states, most of which are characterized by exotic spin excitations with fractional quantum numbers (termed `spinon'). Here, we report neutron scattering measurements that reveal broad spin excitations covering a wide region of the Brillouin zone in a triangular antiferromagnet YbMgGaO4. The observed diffusive spin excitation persists at the lowest measured energy and shows a clear upper excitation edge, which is consistent with the particle-hole excitation of a spinon Fermi surface. Our results therefore point to a QSL state with a spinon Fermi surface in YbMgGaO4 that has a perfect spin-1/2 triangular lattice as in the original proposal of quantum spin liquids.

cond-mat.str-el↗