arXiv subjects

Maya Martinez

Publications and source records attributed to Maya Martinez.

4 recordsLinked to original sources

arXiv2026

A textured polar phase in strained SrTiO3

Quantum materials can harbour hidden phases whose microscopic structures differ from conventional ordered states while reproducing their macroscopic signatures, making them easy to miss. Strontium titanate is a longstanding puzzle of this kind: on cooling it shows every hallmark of an incipient ferroelectric, yet never orders, and is usually described as a quantum paraelectric in which fluctuations suppress ferroelectricity. Here we combine uniaxial strain, single-cycle terahertz excitation and femtosecond x-ray scattering to measure the polar collective modes of strontium titanate as a function of momentum and strain. Under modest tensile strain, we observe a new vibrational mode that emerges not at the Brillouin zone centre, as a ferroelectric transition would require, but at finite wavevector, identifying the ordered state as a polar texture on nanometre length scales rather than a uniform ferroelectric. Unstrained quantum paraelectric strontium titanate is then naturally understood as the disordered precursor of this textured phase, offering a resolution to a decades-old puzzle and illustrating how finite-momentum collective excitations can unmask hidden phases in quantum materials.

cond-mat.mtrl-sci↗

arXiv2025

Modification of the scattering mechanisms in bilayer graphene in proximity to a molecular thin film probed in the mesoscopic regime

Quantum coherent effects can be probed in multilayer graphene through electronic transport measurements at low temperatures. In particular, bilayer graphene is known to be susceptible to quantum interference corrections of the conductivity, presenting weak localization at all electronic densities, and dependent on different scattering mechanisms as well as on the trigonal warping of the electron dispersion near the K and K' valleys. Proximity effects with a molecular thin film influence these scattering mechanisms, which can be quantified through the known theory of magnetoconductance for bilayer graphene. Here, we present weak localization measurements in a copper-phthalocyanine / bilayer graphene / h-BN heterostructure that suggest an important suppression of trigonal warping effects in bilayer graphene (BLG), restoring the manifestation of the chirality of the charge carriers in the localization properties of BLG. Additionally, we observe a charge transfer of 3.6$\times$10$^{12}$cm$^{-2}$ from the BLG to the molecules, as well as a very small degradation of the mobility of the BLG/h-BN heterostructure upon the deposition of copper phthalocyanine (CuPc). The molecular arrangement of the CuPc thin film is characterized in a control sample through transmission electron microscopy, that we relate to the electronic transport results.

cond-mat.mes-hall↗

arXiv2024

Distinct amplitude mode dynamics upon resonant and off-resonant excitation across the charge density wave energy gap in LaTe3 investigated by time- and angle-resolved photoemission spectroscopy

Non-equilibrium states generated by ultrafast laser pulses are characterized by specific phenomena that are not accessible in static measurements. Previous time- and angle-resolved photoemission spectroscopy (TARPES) studies on rare-earth tritelluride materials have revealed the laser-driven melting of the charge density wave order as well as its collective amplitude mode excitation. Variation of the excess energy deposited by optical pumping in the material promises pathways to control the dynamic material response. To this end, we use an optical parametric amplifier to generate a tunable pump photon energy. Studying LaTe3 we compare the dynamics driven by pumping resonantly across the charge density wave energy gap with the effect of pumping at a twice higher photon energy in a TARPES pump-probe experiment. We clearly identify a pump photon energy dependent behavior. At the larger pump photon energy, the excess electronic energy generates lattice heating mediated by e-ph coupling and softening of the amplitude mode frequency from 3 to 2 THz. Remarkably, the resonant pumping across the CDW gap results in a time-independent amplitude mode frequency. We conclude that the resonant excitation across the energy gap excites the amplitude mode selectively while additional electronic excess energy deposited at higher pump photon energy modifies the crystal properties transiently by incoherent dissipative processes.

cond-mat.str-el↗

arXiv2022

Electronic transport mechanisms in a thin crystal of the Kitaev candidate $\alpha$-RuCl$_3$ probed through guarded high impedance measurements

$\alpha$-RuCl$_3$ is considered to be the top candidate material for the experimental realization of the celebrated Kitaev model. It is however known that additional interactions beyond the Kitaev model trigger in $\alpha$-RuCl$_3$, a long-range zigzag antiferromagnetic ground state. In this work, we investigate a nanoflake of $\alpha$-RuCl$_3$ through guarded high impedance measurements aimed at reaching through electronic transport, the regime where the system turns into a zigzag antiferromagnet. We investigated a variety of temperatures (\SI{1.45}{\kelvin} - \SI{175}{\kelvin}) and out-of-plane magnetic fields ranging up to \SI{11}{\tesla}. We found a clear signature of a structural phase transition at $\approx 160$\,K as reported for thin crystals of $\alpha$-RuCl$_3$, as well as a thermally activated behavior at temperatures above $\approx 30$\,K with a characteristic activation energy significantly smaller than the energy gap that we observe for $\alpha$-RuCl$_3$ bulk crystals through our Angle Resolved Photoemission Spectroscopy (ARPES) experiments. Additionally we found that below $\approx 30$\,K, transport is ruled by Efros-Shklovskii (ES) VRH. These observations point to the presence of Coulomb impurities in our thin crystals. Most importantly, our data shows that below the magnetic ordering transition known for bulk $\alpha$-RuCl$_3$ ($\approx 7$\,K), there is a clear deviation from VRH or thermal activation transport mechanisms. Our work demonstrates the possibility of reaching through specialized high impedance measurements, the thrilling ground states predicted for $\alpha$-RuCl$_3$ at low temperatures in the frame of the Kitaev model, and informs about the transport mechanisms in this material in a wide temperature range as well as on important characteristic quantities such as the localization length of the impurities in a thin $\alpha$-RuCl$_3$ crystal.

cond-mat.str-el↗