arXiv subjects

S. Raymond

Publications and source records attributed to S. Raymond.

At least 73 records · Page 4Linked to original sources

arXiv2005

Non-linear exciton spin-splitting in single InAs/GaAs self-assembled quantum structures in ultrahigh magnetic fields

We report on the magnetic field dispersion of the exciton spin-splitting and diamagnetic shift in single InAs/GaAs quantum dots (QDs) and dot molecules (QDMs) up to $B$ = 28 T. Only for systems with strong geometric confinement, the dispersions can be well described by simple field dependencies, while for dots with weaker confinement considerable deviations are observed: most importantly, in the high field limit the spin-splitting shows a non-linear dependence on $B$, clearly indicating light hole admixtures to the valence band ground state.

cond-mat.mes-hall↗

arXiv2005

Low energy spin fluctuations in the heavy fermion compound Ce$_{0.925}$La$_{0.075}$Ru$_{2}$Si$_{2}$

We report inelastic neutron scattering measurements performed on a single crystal of the heavy fermion compound Ce$_{0.925}$La$_{0.075}$Ru$_{2}$Si$_{2}$, which is at the borderline between an antiferromagnetically ordered and a paramagnetic ground state. Intensity maps as a function of wavevector and energy ($0.1<E<1.2$ meV) were obtained at temperatures $T=0.1$ and 2 K, using the time-of-flight spectrometer IRIS. An unexpected saturation of the relaxation rate and static susceptibility of the spin fluctuations is found at low temperatures.

cond-mat.str-el↗

arXiv2004

Inelastic neutron scattering study of single crystal heavy fermion YbAgGe

Single crystals of the heavy-fermion compound YbAgGe have been studied by neutron scattering. The magnetic ordering occurring below T1=0.5 K is characterized by a commensurate propagation vector k=(1/3,0,1/3) and the moments in the basal plane of the hexagonal structure. The dynamic magnetic susceptibility is dominated by quasielastic spin fluctuations with a characteristic energy Gamma of the order of 1 meV. The spins fluctuate predominantly in the basal plane. No spin-wave excitations are observed in the magnetically ordered phase. Below the Kondo temperature, TK=20 K, Gamma shows a strong q dependence for wave vectors along the c* direction, but is q-independent in the basal plane. Gamma shows initially a rapid increase with temperature T at the antiferromagnetic zone center, but follows a standard sqrt(T) law for other q values and for T>TK in general. These observations classify YbAgGe as a well-behaved heavy-fermion compound with a particular q-dependence of the antiferromagnetic spin fluctuations, possibly related to the geometrical frustration of the Yb3+ ions.

cond-mat.str-el↗

arXiv2004

Anomalous scaling behavior of the dynamical spin susceptibility of Ce$_{0.925}$La$_{0.075}$Ru$_{2}$Si$_{2}$

Inelastic neutron scattering measurements have been performed on single crystals of the heavy fermion compound Ce$_{0.925}$La$_{0.075}$Ru$_{2}$Si$_{2}$ in broad energy [0.1, 9.5 meV] and temperature [40 mK, 294 K] ranges in order to address the question of scaling behavior of the dynamical spin susceptibility at the quantum critical point of an itinerant magnetic system. For two wavevectors $\mathbf{Q}$ corresponding to uncorrelated and antiferromagnetically correlated spin fluctuations, it is found that the dynamical spin susceptibility $χ''(\mathbf{Q},E,T)$ is independent of temperature below a cut-off temperature $T_{\mathbf{Q}}$: the spin fluctuation amplitude saturates at low temperatures contrarily to its expected divergence at a quantum critical point. Above $T_{\mathbf{Q}}$, a $\mathbf{Q}$-dependent scaling behavior of the form $Tχ''(\mathbf{Q},E,T) = C_{\mathbf{Q}}f[E/(a_{\mathbf{Q}}T^{β_{\mathbf{Q}}})]$ with $β_{\mathbf{Q}}<1$ is obtained. This scaling does not enter the general framework of quantum phase transition theories, since it is obtained in a high temperature range, where Kondo spin fluctuations depend strongly on temperature.

cond-mat.str-el↗

arXiv2003

Spin dynamics of the ferromagnetic superconductor UGe$_{2}$

Inelastic neutron scattering was used to study the low energy magnetic excitations of the ferromagnetic superconductor UGe$_{2}$. The ferromagnetic fluctuations are of Ising nature with a non-conserved magnetization and have an intermediate behavior between localized and itinerant magnetism.

cond-mat.str-el↗

arXiv2003

Pressure dependence of magnetism in URu2Si2

Neutron-scattering and specific-heat measurements of the heavy-fermion superconductor URu2Si2 under hydrostatic pressure and with Rh-doping [U(Ru{0.98}Rh{0.02})2Si2] show the existence of two magnetic phase transitions. At the second-order phase transition Tm ≈ 17.5 K, a tiny ordered moment is established, while at TM < Tm, a first-order phase transition (under pressure or doping) gives rise to a large moment. The results can be understood in terms of a hidden OP Psi coupled to the ordered moment m, where m and Psi have the same symmetry.

cond-mat.str-el↗

arXiv2003

Spin Fluctuations and Non-Fermi-Liquid Behavior of CeNi_2Ge_2

Neutron scattering shows that non-Fermi-liquid behavior of the heavy-fermion compound CeNi_2Ge_2 is brought about by the development of low-energy spin fluctuations with an energy scale of 0.6 meV. They appear around the antiferromagnetic wave vectors $({1/2} {1/2} 0)$ and $(0 0 {3/4})$ at low temperatures, and coexist with high-energy spin fluctuations with an energy scale of 4 meV and a modulation vector $(0.23, 0.23, {1/2})$. This unusual energy dependent structure of $\text{Im} χ(\bm{Q}, E)$ in $\bm{Q}$ space suggests that quasiparticle bands are important.

cond-mat.str-el↗

arXiv2003

Polarization analysis of the inelastic magnetic scattering in Sr2RuO4

The spin fluctuations in the normal state of the unconventional superconductor Sr2RuO4 have been studied using inelastic neutron scattering with polarization analysis on single crystals. We find that the spin fluctuations are anisotropic with chi_c/chi_ab=2.0 (0.4). No evidence for Q-independent or nearly-ferromagnetic spin fluctuations are found in the energy range 4-22 meV, in contradiction with NMR measurements.

cond-mat.str-el↗

arXiv2003

Phase diagram of heavy fermion systems

The Meccano of heavy fermion systems is shown on different cases going from anomalous monochalcogenides to cerium intermetallic compounds with special focus on the ideal case of the CeRu2Si2 series. Discussion is made in the frame of the interplay between valence, electronic structure (Fermi surface), and magnetism. The nice tools given by the temperature, the pressure, and the magnetic field allow to explore different ground states as well as the slow downhill ''race'' before reaching a Fermi liquid finish line at very low temperature. Experimentally, the Gr"uneisen parameter i.e. the ratio of the thermal expansion by the specific heat is a coloured magic number; its temperature, pressure, and magnetic field dependence is a deep disclosure of competing hierarchies and the conversion of this adaptive matter to external responses.

cond-mat.str-el↗

arXiv2003

Study of low-energy magnetic excitations in single-crystalline CeIn3 by inelastic neutron scattering

Inelastic neutron scattering experiments were performed on single crystals of the heavy-fermion compound CeIn$_{3}$ for temperatures below and above the Néel temperature, $T_N$. In the antiferromagnetically ordered phase, well-defined spin-wave excitations with a bandwidth of 2 meV are observed. The spin waves coexist with quasielastic (QE) Kondo-type spin-fluctuations and broadened crystal-field (CF) excitations below $T_N$. Above $T_N$, only the QE and CF excitations persist, with a weak temperature dependence.

cond-mat.str-el↗

arXiv2002

Polarization dependence of spin excitations in BaCu2Si2O7

The polarization dependence of magnetic excitations in the quasi one-dimensional antiferromagnet BaCu2Si2O7 is studied as a function of momentum and energy transfer. The results of inelastic neutron scattering measurements are directly compared to semi-analytical calculations based on the chain-Mean Field and Random Phase approximations. A quantitative agreement between theoretically calculated and experimentally measured dynamic structure factors of transverse spin fluctuations is obtained. In contrast, substantial discrepancies are found for longitudinal polarization. This behavior is attributed to intrinsic limitations of the RPA that ignores correlation effects.

cond-mat.str-el↗

arXiv2002

Phonon anomalies at the valence transition of SmS : An inelasticX-ray scattering study under pressure

The phonon dispersion curve of SmS under pressure was studied by inelastic x-ray scattering around the pressure-induced valence transition. A significant softening of the longitudinal acoustic modes propagating along the [111] direction was observed spanning a wide $q$ region from ($\frac{2π}{3a},\frac{2π}{3a},\frac{2π}{3a}$) up to the zone boundary as SmS becomes metallic. The largest softening occurs at the zone boundary and stays stable up to the highest measured pressure of 80 kbar while a gradual hardening of the low $q$ modes simultaneously appears. This phonon spectrum indicates favorable conditions for the emergence of pressure-induced superconductivity in SmS.

cond-mat.str-el↗

arXiv2002

Itinerant metamagnetism of CeRu2Si2 : bringing out the dead. Comparison with the new Sr3Ru2O7 case

Focus is given on the macroscopic and microscopic experimental works realized during a decade on the clear case of itinerant metamagnetism in the heavy fermion paramagnetic compound CeRu2Si2 . Emphasis is made on the feedback between the band structure, the exchange coupling and the lattice instability. Sweeps in magnetic field, pressure and temperature feel the pseudogap of this strongly correlated electronic system as well as its equivalent CeRu2Ge2 at a fictitious negative pressure. Some mysteries persist as the complete observation of the FS above the metamagnetic field HM and the detection of the dynamical ferromagnetic fluctuation near HM. The novelty of the bilayer ruthenate Sr3Ru2O7 is discussed by comparison. Despite differences in spin and electronic dimensionality many common trends emerge.

cond-mat.str-el↗

arXiv2001

Spin dynamics in the $S=1/2$ weakly-coupled chains antiferromagnet BaCu$_2$Si$_2$O$_7$

Inelastic neutron scattering is used to identify single-particle and continuum spin excitations in the quasi-one-dimensional $S=1/2$ antiferromagnet \ba. In the data analysis, close attention is given to resolution effects. A gap in the continuum spectrum at $Δ_c=4.74.8$ meV is directly observed. The gap energy is in excellent agreement with existing theoretical predictions. Below the gap, the spectrum is dominated by sharp accoustic spin wave excitations.

cond-mat.str-el↗

arXiv2001

Pressure dependence of the spin dynamics around a quantum critical point : An inelastic neutron scattering study of Ce0.87La0.13Ru2Si2

Inelastic neutron scattering experiments performed on a single crystal of the antiferromagnetic compound Ce$_{0.87}$La$_{0.13}$Ru$_{2}$Si$_{2}$ under applied pressures of up to 5 kbar are reported. A quantum critical point is reached at around 2.6 kbar where long-range magnetic order disappears. The variation of the characteristic energy scales with respect to temperature and pressure is followed and found to saturate in the ordered phase.

cond-mat.str-el↗

arXiv2000

Magnetic order and spin-waves in the quasi-1D S=1/2 antiferromagnet ${\bf BaCu_{2}Si_{2}O_{7}}$

Elastic and inelastic neutron scattering were used to study the ordered phase of the quasi-one-dimensional spin-1/2 antiferromagnet ${\rm BaCu_{2}Si_{2}O_{7}}$. The previously proposed model for the low-temperature magnetic structure was confirmed. Spin wave dispersion along several reciprocal-space directions was measured and inter-chain, as well as in-chain exchange constants were determined. A small gap in the spin wave spectrum was observed and attributed to magnetic anisotropy effects. The results are discussed in comparison with existing theories for weakly-coupled quantum spin chain antiferromagnets.

cond-mat.str-el↗

arXiv2000

Pressure-induced residual resistivity anomaly in CeCu_5Au

The electrical resistivity of the magnetically ordered CeCu_5Au has been investigated under pressure up to 8.5 GPa. In the magnetically ordered region (p<3.4 GPa) the residual resistivity rho_0 shows a pronounced maximum as a function of pressure. Even in the nonmagnetic region rho_0 decreases monotonically by more than a factor of three. These two effects can be qualitatively explained in terms of the interplay of pressure, magnetism and disorder in a strongly correlated electron system with weak disorder.

cond-mat.str-el↗

arXiv2000

Energy separation of single-particle and continuum states in a S=1/2 weakly-coupled chains antiferromagnet

Inelastic neutron scattering is used to study transverse-polarized magnetic excitations in the quasi-one-dimensional S=1/2 antiferromagnet BaCu_2Si_2O_7, where the saturation value for the Néel order parameter is $m_0=0.12 μ_{\rm B}$ per spin. At low energies the spectrum is totally dominated by resolution-limited spin wave-like excitations. An excitation continuum sets in above a well-defined threshold frequency. Experimental results are discussed in the context of current theories for weakly-interacting quantum half-integer spin chains.

cond-mat.str-el↗