arXiv subjects

S. Nakamae

Publications and source records attributed to S. Nakamae.

11 recordsLinked to original sources

arXiv2020

Phase diagram of a three-dimensional dipolar model on a FCC lattice

The magnetic phase diagram at zero external field of an ensemble of dipoles with uniaxial anisotropy on a FCC lattice is investigated from tempered Monte Carlo simulations. The uniaxial anisotropy is characterized by a random distribution of easy axes and its magnitude $λ_u$ is the driving force of disorder and consequently frustration. The phase diagram, separating the paramagnetic, ferromagnetic, quasi long range ordered ferromagnetic and spin-glass regions is thus considered in the temperature, $λ_u$ plane. This system is aimed at modeling the magnetic phase diagram of supracrystals of magnetic nanoparticles.

cond-mat.mtrl-sci↗

arXiv2015

Experimental Study of Thermodiffusion and Thermoelectricity in Charged Colloids

The Seebeck and Soret coefficients of ionically stabilized suspension of maghemite nanoparticles in dimethyl sulfoxide are experimentally studied as a function of nanoparticle volume fraction. In the presence of a temperature gradient, the charged colloidal nanoparticles experience both thermal drift due to their interactions with the solvent molecules and electric forces proportional to the internal thermoelectric field. The resulting thermodiffusion of nanoparticles is observed through Forced Rayleigh scattering, while the thermoelectric field is accessed through voltage measurements in a thermocell. Both techniques provide independent estimates of nanoparticle's entropy of transfer as high as 75 meV/K. Such a property may be used to improve the thermoelectric coefficients in liquid thermocells.

cond-mat.soft↗

arXiv2011

Huge Seebeck coefficients in non-aqueous electrolytes

The Seeebeck coefficients of the non-aqueous electrolytes tetrabutylammonium nitrate, tetraoctylphosphonium bromide and tetradodecylammonium nitrate in 1-octanol, 1-dodecanol and ethylene-glycol are measured in a temperature range from T=30 to T=45 C. The Seebeck coefficient is generally of the order of a few hundreds of microvolts per Kelvin for aqueous solution of inorganic ions. Here we report huge values of 7 mV/K at 0.1M concentration for tetrabutylammonium nitrate in 1-dodecanol. These striking results open the question of unexpectedly large kosmotrope or "structure making" effects of tetraalkylammonium ions on the structure of alcohols.

cond-mat.soft↗

arXiv2010

Noise Measurement of Interacting Ferromagnetic Particles with High Resolution Hall Microprobes

We present our first experimental determination of the magnetic noise of a superspinglass made of < 1 pico-liter frozen ferrofluid. The measurements were performed with a local magnetic field sensor based on Hall microprobes operated with the spinning current technique. The results obtained, though preliminary, qualitatively agree with the theoretical predictions of Fluctuation-Dissipation theorem (FDT) violation [1].

cond-mat.dis-nn↗

arXiv2009

Growth of a dynamical correlation length in an aging superspin glass

We report on zero field cooled magnetization relaxation experiments on a concen- trated frozen ferrofluid exhibiting a low temperature superspin glass transition. With a method initially developed for spin glasses, we investigate the field dependence of the relaxations that take place after different aging times. We extract the typical number of correlated spins involved in the aging dynamics. This brings important insights into the dynamical correlation length and its time growth. Our results, consistent with expressions obtained for spin glasses, extend the generality of these behaviours to the class of superspin glasses. Since the typical flipping time is much larger for superspins than for atomic spins, our experiments probe a time regime much closer to that of numerical simulations.

cond-mat.dis-nn↗

arXiv2007

Low temperature magnetization of the S=1/2 kagome antiferromagnet ZnCu_3(OH)_6Cl_2

The dc-magnetization of the unique S=1/2 kagome antiferromagnet Herbertsmithite has been measured down to 0.1K. No sign of spin freezing is observed in agreement with former muSR and ac-susceptibility results. The low temperature magnetic response is dominated by a defect contribution which exhibits a new energy scale $\simeq 1$ K, likely reflecting the coupling of the defects. The defect component is saturated at low temperature by H>8T applied magnetic fields which enables us to estimate an upper bound for the non saturated intrinsic kagome susceptibility at T=1.7K.

cond-mat.str-el↗

arXiv2007

Effect of premelting on conductivity of DNA-lipid films

We have measured temperature dependent (between 20 and 80 C) electrical conductivity and molecular structure (Raman spectroscopy) of DNA-lipid cast film. Our findings show that the conductivity is strongly influenced by premelting effects in the molecular structure starting near physiological temperatures (~40 C), prior to the global DNA denaturation.

cond-mat.soft↗

arXiv2005

Intrinsic Low Temperature Paramagnetism in B-DNA

We present experimental study of magnetization in $λ$-DNA in conjunction with structural measurements. The results show the surprising interplay between the molecular structures and their magnetic property. In the B-DNA state, $λ$-DNA exhibits paramagnetic behaviour below 20 K that is non-linear in applied magnetic field whereas in the A-DNA state, remains diamagnetic down to 2 K. We propose orbital paramagnetism as the origin of the observed phenomena and discuss its relation to the existence of long range coherent transport in B-DNA at low temperature.

cond-mat.other↗

arXiv2002

The ground state of heavily-overdoped non-superconducting La$_{2-x}$Sr$_x$CuO$_4$

We report detailed thermodynamic and transport measurements for non-superconducting La$_{1.7}$Sr$_{0.3}$CuO$_4$. Collectively, these data reveal that a highly-correlated Fermi-liquid ground state exists in La$_{2-x}$Sr$_x$CuO$_4$ beyond the superconducting dome, and confirm that charge transport in the cuprates is dominated at finite temperatures by intense electron-electron scattering.

cond-mat.str-el↗

arXiv2000

Effect of controlled disorder on quasiparticle thermal transport in Bi$_2$Sr$_2$CaCu$_2$O$_8$

Low temperature thermal conductivity, $κ$, of optimally-doped Bi2212 was studied before and after the introduction of point defects by electron irradiation. The amplitude of the linear component of $κ$ remains unchanged, confirming the universal nature of heat transport by zero-energy quasiparticles. The induced decrease in the absolute value of $κ$ at finite temperatures allows us to resolve a nonuniversal term in $κ$ due to conduction by finite-energy quasiparticles. The magnitude of this term provides an estimate of the quasiparticle lifetime at subkelvin temperatures.

cond-mat.supr-con↗

arXiv2000

Absence of residual quasiparticle conductivity in the underdoped cuprate YBa2Cu4O8

We report here measurements of the in-plane thermal conductivity K(T) of the underdoped cuprate YBa2Cu4O8 (Y124) below 1K. K(T) is shown to follow a simple, phononic T^3 dependence at the lowest temperatures for both current directions, with a negligible linear, quasiparticle contribution. This observation is in marked contrast with behavior reported in optimally doped cuprates, and implies that extended zero-energy (or low energy) low-energy quasiparticles are absent in YBa2Cu4O8 at low temperatures.

cond-mat.supr-con↗