Scaling law of Wolff cluster surface energy

We study the scaling properties of the clusters grown by the Wolff algorithm on seven different Sierpinski-type fractals of Hausdorff dimension $1 < d_f \le 3$ in the framework of the Ising model. The mean absolute value of the surface energy of Wolff cluster follows a power law with respect to the lattice size. Moreover, we investigate the probability density distribution of the surface energy of Wolff cluster and are able to establish a new scaling relation. It enables us to introduce a new exponent associated to the surface energy of Wolff cluster. Finally, this new exponent is linked to a dynamical exponent via an inequality.Comment: 12 pages, 3 figures. To appear in PR

Dynamical transport properties of NbSe3_3 with simultaneous sliding of both charge density waves

Measurements of the nonlinear conductivity in NbSe$_3$ when the high-T and the low-T charge-density waves (CDWs) are simultaneously sliding have been performed. It is shown that the threshold electric field, $E_{t1}$, for depinning the high-T CDW increases 4 - 5 times at the temperature at which the low-T CDW is formed, indicating the strong pinning effect resulting from the interaction between both CDWs. Under application of a radio-frequency (rf) field, Shapiro steps are never observed simultaneously for both CDWs. At the electric field less then one for high-T CDW sliding only Sapiro steps for low-T CDW were observed, and at higher field only Shapiro steps for high-T CDW exist.Comment: 5 pages, 6 figures, accepted in PR

Ferroelectric Mott-Hubbard phase in organic conductors

We present key issues of related phenomenons of the Ferroelectricity and the Charge Disproportionation in organic metals. In (TMTTF_2X the dielectric susceptibility demonstrates clear cases of the ferroelectric and anti-ferroelectric phase transitions. Both the susceptibility and the conductivity prove independence and occasional coexistence of "structurless" ferroelectric transitions and usual "anionic" ones. Their sequence gives access to physics of three types of solitons emerging upon cooling via several steps of symmetry breaking. The theory invokes a concept of the Combined Mott-Hubbard State which focuses upon weak processes of electronic Umklapp scattering coming from both the build-in nonequivalence of bonds and the spontaneous one of sites. We propose that the charge ordering in its form of the ferroelectricity exists hiddenly even in the Se subfamily (TMTSF)_2X, giving rise to the unexplained yet low frequency optical peak and the enhanced pseudogap.Comment: Proceedings of the ICSM 200

Charge density wave transport in submicron antidot arrays in NbSe3

We demonstrate for the first time that a periodic array of submicrometer holes (antidots) can be patterned into thin single NbSe3 crystals. We report on the study of charge density wave (CDW) transport of the network of mesoscopic units between antidots. Size of the elementary unit can be as small as 0.5 micron along the chain axis and (0.2 micron) x (0.3 micron) in cross section. We observe size effects for Ohmic residual resistance and in CDW transport current-voltage characteristics in submicronic networks.Comment: 4 pages with 1 table and 10 figures. Submitted to European Physical Journa

Recent results on energy relaxation in disordered charge and spin density waves

We briefly review different approaches used recently to describe collective effects in the strong pinning model of disordered charge and spin density waves, in connection with the CRTBT very low temperature heat relaxation experiments.Comment: 4 pages, invited talk at ECRYS-200

Quantum critical point and superconducting dome in the pressure phase diagram of o-TaS3

We measure the electrical resistance of o-TaS3 between 1K and 300K under pressures up to 20GPa. We observe a gradual decrease of the charge density wave transition temperature with increasing pressure P following a mean-field quantum fluctuation power law with a quantum critical point at a pressure Pc = 11.5GPa. Around the quantum critical point we observe a superconducting dome with a maximum superconducting transition temperature Tc = 3.1K. Such dome is similar to superconducting domes around other types of order suggesting that the QCP is directly responsible for the enhancement of superconductivity through a universal mechanism still not well understood.Comment: To be published in PRB as a Rapid Communication. 11 pages with 4 figure

Slow relaxation experiments in disordered charge and spin density waves: collective dynamics of randomly distributed solitons

We show that the dynamics of disordered charge density waves (CDWs) and spin density waves (SDWs) is a collective phenomenon. The very low temperature specific heat relaxation experiments are characterized by: (i) ``interrupted'' ageing (meaning that there is a maximal relaxation time); and (ii) a broad power-law spectrum of relaxation times which is the signature of a collective phenomenon. We propose a random energy model that can reproduce these two observations and from which it is possible to obtain an estimate of the glass cross-over temperature (typically $T_g \simeq 100 - 200$ mK). The broad relaxation time spectrum can also be obtained from the solutions of two microscopic models involving randomly distributed solitons. The collective behavior is similar to domain growth dynamics in the presence of disorder and can be described by the dynamical renormalization group that was proposed recently for the one dimensional random field Ising model [D.S. Fisher, P. Le Doussal and C. Monthus, Phys. Rev. Lett. {\bf 80}, 3539 (1998)]. The typical relaxation time scales like $\tau^{\rm typ} \sim \tau_0 \exp{(T_g/T)}$. The glass cross-over temperature $T_g$ related to correlations among solitons is equal to the average energy barrier and scales like $T_g \sim 2 x \xi_0 \Delta$. $x$ is the concentration of defects, $\xi_0$ the correlation length of the CDW or SDW and $\Delta$ the charge or spin gap.Comment: 20 pages, 16 figure

Charge modulations vs. strain waves in resonant x-ray scattering

A method is described for using resonant x-ray scattering to separately quantify the charge (valence) modulation and the strain wave associated with a charge density wave. The essence of the method is a separation of the atomic form factor into a "raw" amplitude, fR(w), and a valence-dependent amplitude, fD(w), which in many cases may be determined independently from absorption measurements. The advantage of this separation is that the strain wave follows the quantity |fR(w) + fD(w)|^2 whereas the charge modulation follows only |fD(w)|^2. This allows the two distinct modulations to be quantified separately. A scheme for characterizing a given CDW as Peierls-like or Wigner-like naturally follows. The method is illustrated for an idealized model of a one-dimensional chain.Comment: 6 pages, 4 figure