arXiv subjects

M. -A. Measson

Publications and source records attributed to M. -A. Measson.

14 recordsLinked to original sources

arXiv2023

Magneto-optical sensing of the pressure driven magnetic ground states in bulk CrSBr

Competition between exchange interactions and magnetocrystalline anisotropy may bring new magnetic states that are of great current interest. An applied hydrostatic pressure can further be used to tune their balance. In this work we investigate the magnetization process of a biaxial antiferromagnet in an external magnetic field applied along the easy axis. We find that the single metamagnetic transition of the Ising type observed in this material under ambient pressure transforms under hydrostatic pressure into two transitions, a first-order spin flop transition followed by a second order transition towards a polarized ferromagnetic state near saturation. This reversible tuning into a new magnetic phase is obtained in layered bulk CrSBr at low temperature by varying the interlayer distance using high hydrostatic pressure, which efficiently acts on the interlayer magnetic exchange, and is probed by magneto-optical spectroscopy.

cond-mat.mes-hall↗

arXiv2022

Spatially resolved optical spectroscopy in extreme environment of low temperature, high magnetic fields and high pressure

We present an experimental set-up developed to perform optical spectroscopy experiments (Raman scattering and photoluminescence measurements) with a micrometer spatial resolution, in an extreme environment of low temperature, high magnetic field and high pressure. This unique experimental setup, to the best of our knowledge, allows us to explore deeply the phase diagram of condensed matter systems by tuning independently these three thermodynamic parameters, while monitoring the low-energy excitations (electronic, phononic or magnetic excitations), to spatially map the Raman scattering response or to investigate objects with low dimensions. We apply this technique to bulk FePS3, a layered antiferromagnet with a Neel temperature of T = 120 K.

cond-mat.mtrl-sci↗

arXiv2017

Strain and Magnetic Field Induced Spin-Structure Transitions in Multiferroic BiFeO3

The magnetic-field-dependent spin ordering of strained BiFeO3 films is determined using nuclear resonant scattering and Raman spectroscopy. The critical field required to destroy the cycloidal modulation of the Fe spins is found to be significantly lower than in the bulk, with appealing implications for field-controlled spintronic and magnonic devices.

cond-mat.mtrl-sci↗

arXiv2016

Charge induced nematicity in FeSe

The spontaneous appearance of nematicity, a state of matter that breaks rotation but not translation symmetry, is one of the most intriguing property of the iron based superconductors (Fe SC), and has relevance for the cuprates as well. Establishing the critical electronic modes behind nematicity remains however a challenge, because their associated susceptibilities are not easily accessible by conventional probes. Here using FeSe as a model system, and symmetry resolved electronic Raman scattering as a probe, we unravel the presence of critical charge nematic fluctuations near the structural / nematic transition temperature, T$_S\sim$ 90 K. The diverging behavior of the associated nematic susceptibility foretells the presence of a Pomeranchuk instability of the Fermi surface with d-wave symmetry. The excellent scaling between the observed nematic susceptibility and elastic modulus data demonstrates that the structural distortion is driven by this d-wave Pomeranchuk transition. Our results make a strong case for charge induced nematicity in FeSe.

cond-mat.supr-con↗

arXiv2016

Collapse of the Normal State Pseudogap at a Lifshitz Transition in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ Cuprate Superconductor

We report a fine tuned doping study of strongly overdoped Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ single crystals using electronic Raman scattering. Combined with theoretical calculations, we show that the doping, at which the normal state pseudogap closes, coincides with a Lifshitz quantum phase transition where the active hole-like Fermi surface becomes electron-like. This conclusion suggests that the microscopic cause of the pseudogap is sensitive to the Fermi surface topology. Furthermore, we find that the superconducting transition temperature is unaffected by this transition, demonstrating that their origins are different on the overdoped side.

cond-mat.supr-con↗

arXiv2015

Three energy scales in the superconducting state of hole-doped cuprates detected by electronic Raman scattering

We explored by electronic Raman scattering the superconducting state of Bi-2212 single crystal by performing a fine tuned doping study. We found three distinct energy scales in A1g, B1g and B2g symmetries which show three distinct doping dependencies. Above p=0.22 the three energies merge, below p=0.12, the A1g scale is no more detectable while the B1g and B2g scales become constant in energy. In between, the A1g and B1g scales increase monotonically with under-doping while the B2g one exhibits a maximum at p=0.16. The three superconducting energy scales appear to be an universal feature of hole-doped cuprates. We propose that the non trivial doping dependence of the three scales originates from Fermi surface topology changes and reveals competing orders inside the superconducting dome.

cond-mat.supr-con↗

arXiv2013

Observation of incipient charge nematicity in Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$

Using electronic Raman spectroscopy, we report direct measurements of charge nematic fluctuations in the tetragonal phase of strain-free Ba(Fe$_{1-x}$Co$_{x})_{2}$As$_{2}$ single crystals. The strong enhancement of the Raman response at low temperatures unveils an underlying charge nematic state that extends to superconducting compositions and which has hitherto remained unnoticed. Comparison between the extracted charge nematic susceptibility and the elastic modulus allows us to disentangle the charge contribution to the nematic instability, and to show that charge nematic fluctuations are weakly coupled to the lattice.

cond-mat.supr-con↗

arXiv2013

Exploring the Dark Side of Cuprate Superconductors: s-wave Symmetry of the Pseudogap

We reveal the full energy-momentum structure of the pseudogap of underdoped high-Tc cuprate superconductors. Our combined theoretical and experimental analysis explains the spectral-weight suppression observed in the B2g Raman response at finite energies in terms of a pseudogap appearing in the single-electron excitation spectra above the Fermi level in the nodal direction of momentum space. This result suggests an s-wave pseudogap (which never closes in the energy-momentum space), distinct from the d-wave superconducting gap. Recent tunneling and photoemission experiments on underdoped cuprates also find a natural explanation within the s-wave-pseudogap scenario.

cond-mat.str-el↗

arXiv2012

Lattice and spin excitations in multiferroic h-YbMnO3

Lattice and spin excitations have been studied by Raman scattering in hexagonal YbMnO3 single crystals. The temperature dependences of the phonon modes show that the E2 mode at 256 cm-1 related to the displacement of Mn and O ions in a-b plane is coupled to the spin order. The A1 phonon mode at 678 cm-1 presents a soft mode behavior at the Neel temperature. Connected to the motion of the apical oxygen ions along the c direction, this mode controls directly the Mn-Mn interactions between adjacent Mn planes and the superexchange path. Crystal field and magnon mode excitations have been identified. The temperature investigation of the spin excitations shows that the spin structure is strongly influence by the Yb-Mn interaction. Under a magnetic field along the c axis, we have investigated the magnetic reordering and its impact on the spin excitations.

cond-mat.str-el↗

arXiv2012

New insights into the phase diagram of the copper oxide superconductors from electronic Raman scattering

Mechanism of unconventional superconductivity is still unknown even if more than 25 years have been passed since the discovery of high-Tc cuprate superconductors by J.G. Bednorz and K. A. Muller. Here, we explore the cuprate phase diagram by electronic Raman spectroscopy and shed light on the superconducting state in hole doped cuprates. Namely, how superconductivity and the critical temperature Tc are impacted by the pseudogap.

cond-mat.supr-con↗

arXiv2012

Electromagnon and phonon excitations in multiferroic TbMnO3

We have performed Raman measurements on TbMnO3 single crystal under magnetic field along the three crystallographic directions. The flip of the spin spiral plane creates an electromagnon excitation. In addition to the electromagnons induced by the Heisenberg coupling, we have detected the electromagnon created by the Dzyaloshinskii-Moriya interaction along the c axis. We have identified all the vibrational modes of TbMnO3. Their temperature dependences show that only one phonon observed along the polarization axis is sensitive to the ferroelectric transition. This mode is tied to the Tb3+ ion displacements that contribute to the ferroelectric polarization.

cond-mat.str-el↗

arXiv2007

Double superconducting transition in the filled skutterudite PrOs4Sb12 and sample characterizations

A thorough characterization of many samples of the filled skutterudite compound PrOs4Sb12 is provided. We find that the double superconducting transition in the specific heat Tc1~1.89K and Tc2~1.72K tends to appear in samples with a large residual resistivity ratio, large specific heat jump at the superconducting transition and with the highest absolute value of the specific heat above Tc1. However, we present evidence which casts doubt on the intrinsic nature of the double superconducting transition. The ratio of the two specific heat jumps ΔC(Tc1)/ΔC(Tc2) shows a wide range of values on crystals from different batches but also within the same batch. This ratio was strongly reduced by polishing a sample down to 120um. Remarkably, three samples exhibit a single sharp transition of ~15mK in width at Tc~1.7K. The normalized specific heat jump (C-Cnormal)/Cnormal at Tc of two of them is higher than ~32% so larger than the sum of the two specific heat jumps when a double transition exists. As an evidence of better quality, the slope in the transition is at least two time steeper. We discuss the origins of the double transition; in particular we consider, based on X-ray diffraction results, a scenario involving Pr-vacancies. The superconducting phase diagram under magnetic field of a sample with a single transition is fitted with a two-band model taking into account the good values for the gap as deduced from thermal conductivity measurements.

cond-mat.str-el↗

arXiv2005

Direct Observation of Quadrupolar Excitons in the Heavy-Fermion Superconductor PrOs$_{4}$Sb$_{12}$

We report inelastic neutron scattering experiments performed to investigate the low energy magnetic excitations on single crystals of the heavy-fermion superconductor PrOs$_{4}$Sb$_{12}$. The observed excitation clearly softens at a wave vector Q = (1,0,0), which is the same as the modulation vector of the field-induced antiferro-quadrupolar ordering, and its intensity at Q = (1,0,0) is smaller than that around the zone center. This result directly evidences that this excitonic behavior is derived mainly from nonmagnetic quadrupolar interactions. Furthermore, the narrowing of the linewidths of the excitations below the superconducting transition temperature indicates the close connection between the superconductivity and the excitons.

cond-mat.str-el↗

arXiv2004

Superconducting phase diagram of the filled skuterrudite PrOs4Sb12

We present new measurements of the specific heat of the heavy fermion superconductor PrOs4Sb12, on a sample which exhibits two sharp distinct anomalies at Tc1= 1.89K and Tc2= 1.72K. They are used to draw a precise magnetic field-temperature superconducting phase diagram of PrOs4Sb12 down to 350 mK. We discuss the superconducting phase diagram of PrOs4Sb12 and its possible relation with an unconventional superconducting order parameter. We give a detailed analysis of Hc2(T), which shows paramagnetic limitation (a support for even parity pairing) and multiband effects.

cond-mat.supr-con↗