11 research outputs found
Probing the Ionic Dielectric Constant Contribution in the Ferroelectric Phase of the Fabre-Salts
In strongly correlated organic materials it has been pointed out that
charge-ordering could also achieve electronic ferroelectricity at the same
critical temperature . A prototype of such phenomenon are the quasi-one
dimensional (TMTTF) Fabre-salts. However, the stabilization of a
long-range ferroelectric ground-state below requires the break of
inversion symmetry, which should be accompanied by a lattice deformation. In
this work we investigate the role of the monovalent counter-anion in such
mechanism. For this purpose, we measured the quasi-static dielectric constant
along the -axis direction, where layers formed by donors and anions
alternate. Our findings show that the ionic charge contribution is three orders
of magnitude lower than the intra-stack electronic response. The
dielectric constant () probes directly the charge response of
the monovalent anion , since the anion mobility in the structure should help
to stabilize the ferroelectric ground-state. Furthermore, our
measurements %conjugated with earlier investigations of the lattice
thermal expansion, show that the dielectric response is thermally broaden below
if the ferroelectric transition occurs in the temperature range where
the anion movement begin to freeze in their methyl groups cavity. In the
extreme case of the PF-H salt, where occurs at the freezing
point, a relaxor-type ferroelectricity is observed. Also, because of the slow
kinetics of the anion sub-lattice, global hysteresis effects and reduction of
the charge response upon successive cycling are observed. In this context, we
propose that anions control the order-disorder or relaxation character of the
ferroelectric transition of the Fabre-salts.Comment: 8 pages, 7 figures. To appear in Physical Review
Giant caloric effects close to critical end point
The electrocaloric effect (ECE), i.e., the reversible temperature change due
to the adiabatic variation of the electric field, is of great interest due to
its potential technological applications. Based on entropy arguments, we
present a new framework to attain giant ECE. Our findings are fourfold: ) we
employ the recently-proposed electric Gr\"uneisen parameter to
quantify the ECE and discuss its advantages over the existing so-called
electrocaloric strength; ) prediction of giant caloric effects to
critical end point; ) proposal of potential key-ingredients to
enhance the ECE; ) demonstration of as a proper parameter to
probe quantum ferroelectricity in connection with the celebrated Barrett's
formula. Our findings enable us to interpret the recently-reported large ECE at
room-temperature in oxide multilayer capacitors [Nature 575, 468 (2019)],
paving thus the way for new venues in the field.Comment: 21 pages, 3 figures, 1 tabl
Gr\"uneisen parameter as an entanglement compass
The Gr\"uneisen ratio , i.e., the singular part of the ratio of
thermal expansion to the specific heat, has been broadly employed to explore
both finite- and quantum critical points (QCPs). For a genuine quantum phase
transition (QPT), thermal fluctuations are absent and thus the thermodynamic
cannot be employed. We propose a quantum analogue to that
computes entanglement as a function of a tuning parameter and show that QPTs
take place only for quadratic non-diagonal Hamiltonians. We showcase our
approach using the quantum 1D Ising model with transverse field and Kane's
quantum computer. The slowing down of the dynamics and thus the ``creation of
mass'' close to any QCP/QPT is also discussed.Comment: 5 pages, 3 figures, comments are wellcome
Estudo das propriedades de materiais supercondutores
Superconductivity was discovered by the dutch physicist Heike Kamerlingh Onnes (1853 1926) employing liquefied 4He to investigate the the behavior of the electrical resistance of a mercury (Hg) sample cooled until 4 K, noticing that the electrical resistance became zero below a certain critical temperature. The main goal of this bachelor work is to review some concepts of modern Physics, discuss some properties of superconducting materials and perform a brief discussion about the BCS theory and its predictions. Furthermore, a literature review of the binary alloy FeSe1x was made to explore phases, since one of them superconducts below 8.5 KO fenĂŽmeno da supercondutividade foi descoberto pelo fĂsico holandĂȘes Heike Kamerlingh Onnes (1853 1926) utilizando 4He liquefeito para monitorar o comportamento da resistĂȘncia elĂ©trica de uma amostra de mercĂșrio (Hg) resfriada atĂ© a temperatura de 4 K, observando que a resistĂȘncia elĂ©trica do Hg tornava-se zero abaixo de uma temperatura crĂtica. O objetivo principal deste trabalho de conclusĂŁo de curso Ă© fazer uma breve revisĂŁo de FĂsica Moderna, discutir algumas propriedades dos materiais supercondutores e realizar uma breve discussĂŁo sobre a teoria BCS e suas prediçÔes. Adicionalmente foi realizada uma revisĂŁo da literatura sobre a liga binĂĄria FeSe1x com a finalidade de explorar as fases da mesma, uma vez que uma delasĂ© supercondutora abaixo de 8,5
Probing the ionic dielectric constant contribution in the ferroelectric phase of the Fabre salts
Exploring the expansion of the universe using the GrĂŒneisen parameter
For a perfect fluid, pressure p and energy density Ï are related via the equation of state (EOS) Ï=p/Ï, where Ï is the EOS parameter, being its interpretation usually constrained to a numerical value for each universe era. Here, based on the MieâGrĂŒneisen EOS, we show that Ï is recognized as the effective GrĂŒneisen parameter Îeff, whose singular contribution, the so-called GrĂŒneisen ratio Î, quantifies the barocaloric effect. Our analysis suggests that the negative p associated with dark-energy implies a metastable state and that in the dark-energy-dominated era Ï is time-dependent, which reinforces recent proposals of a time-dependent cosmological constant. Furthermore, we demonstrate that Îeff is embodied in the energyâmomentum stress tensor in the Einstein field equations, enabling us to analyse, in the frame of an imperfect fluid picture, anisotropic effects of the universe expansion. We propose that upon going from decelerated- to accelerated-expansion, a phase transition-like behaviour can be inferred. Yet, our analysis in terms of entropy, Î, and a by us adapted version of Avramov/Casaliniâs model to Cosmology unveil hidden aspects related to the expansion of the universe. Our findings pave the way to interpret cosmological phenomena in connection with concepts of condensed matter Physics via Îeff