arXiv subjects

Satoshi Tanda

Publications and source records attributed to Satoshi Tanda.

At least 19 recordsLinked to original sources

arXiv2026

Landau Theory for Commensurate Charge-Density Waves Coupled to Uniform Lattice Deformation

We formulate a minimal Landau theory for a charge-density wave (CDW) whose commensurability is defined with respect to a deformed lattice. The motivation is provided by recent observations on an isolated single NbS$_3$ chain, which exhibits a commensurate CDW state accompanied by a $6\%$ shrinkage of the lattice constant. A uniform stretch $a_0\to a_0(1+\varepsilon)$ changes the reciprocal lattice wave number to $G(\varepsilon)=G_0/(1+\varepsilon)$, so that an $N$-fold commensurate CDW has the wave number $Q_\mathrm{C}(\varepsilon)=G(\varepsilon)/N$, whereas the wave number $Q_\mathrm{IC}$ favored by the incommensurate instability remains fixed. We propose an amplitude-strain free energy for both $N=3$ and $N=4$, in which the CDW induces a finite uniform strain by relieving the mismatch between $Q_\mathrm{C}(\varepsilon)$ and $Q_\mathrm{IC}$. The mismatch is shared between the CDW and the lattice in a proportion set by their stiffness ratio; since the CDW stiffness grows with the CDW amplitude, the lattice takes up an increasing share of the mismatch as the CDW develops. Our results suggest a reexamination of lock-in theories and of strain-tuning experiments on density-wave systems.

cond-mat.other↗

arXiv2026

Induced discommensurations in the lock-in transition of charge-density waves

We studied McMillan's free energy of the lock-in transition in charge-density waves. The wave profiles near the critical value were obtained by numerical annealing. First, we demonstrated that our method reproduces the previous studies. The obtained wave profiles include discommensurations near the critical value. Then, we calculated possible wave profiles in the commensurate state. We found that discommensurations are able to be excited in the commensurate state, leading the system to turn into an incommensurate state. We proposed that these wave profiles result from topological invariants. Moreover, excitation of the discommensurations is favorable for the direction to the original wavelength of the incommensurate state. This is attributed to the nature of McMillan's free energy. The current-induced incommensurations, which we discovered with the diffraction study of $o$-TaS$_3$ et al., J. Phys. Soc. Jpn. 77, 093708 (2008)], is consistent with this study.

cond-mat.str-el↗

arXiv2025

Representations of Josephson junction on the unit circle and the derivations of Mathieu operators and Fraunhofer patterns

The Hamiltonian J of the Josephson junction is introduced as a self-adjoint operator on l2 tensor l2. It is shown that J can also be realized as a self-adjoint operator HS1 on L2(S1) tensor L2(S1), from which a Mathieu operator given by "-d^2/d{\theta}^2 - 2{\alpha} cos {\theta}" is derived. A fiber decomposition of HS1 with respect to the total particle number is established, and the action on each fiber is analyzed. In the presence of a magnetic field, a phase shift defines the magnetic Josephson junction Hamiltonian HS1({\Phi}) and the Josephson current IS1({\Phi}). For a constant magnetic field inducing a local phase shift {\Phi}(x), the corresponding local current IS1({\Phi}(x)) is computed, and it is proved that the Fraunhofer pattern arises naturally.

math-ph↗

arXiv2025

Bose glass in Ca$_2$RuO$_4$ nanofilms

Weak localization of bosons can give rise to an exotic quantum phase known as a Bose glass, characterized by the absence of global phase coherence yet finite conductivity. This phase is crucial in understanding the interplay between disorder, interactions, and superconductivity, especially in two-dimensional and strongly correlated systems. Here we report the presence of the Bose glass phase in the weak localization region of ruthenium oxide Ca$_2$RuO$_4$. The electrical resistance exhibits a characteristic logarithmic temperature dependence in this phase, $\rho \sim \ln(1/T)$. Through $\beta$-function scaling analysis, we observed "vertical flow" indicating unconventional scaling behavior associated with localized bosonic states. Our results suggest the existence of bosons-Cooper pairs-persisting up to high temperatures around 220 K and that these bosons undergo weak localization. In the Bose glass phase, vortices are found to have a dual relationship with the localized Cooper pairs, enabling their motion and resulting in finite resistance despite the presence of bosonic order. We identified two quantum critical points: one between the Bose glass and superconducting phases and another between the Bose glass and Mott insulating phases, allowing us to extract the corresponding quantum sheet resistances. We revealed that the ground state of the Ca$_2$RuO$_4$ changes depending on the localization strength. Thinning the Ca$_2$RuO$_4$ corresponds to controlling the electronic correlation by relieving the distortion in RuO$_6$ octahedra. These findings offer significant insights into the interplay between electronic correlations and bosonic transport, with important implications for studying high-temperature superconductors based on perovskite structures.

cond-mat.str-el↗

arXiv2024

SmmPack: Obfuscation for SMM Modules with TPM Sealed Key

System Management Mode (SMM) is the highest-privileged operating mode of x86 and x86-64 processors. Through SMM exploitation, attackers can tamper with the Unified Extensible Firmware Interface (UEFI) firmware, disabling the security mechanisms implemented by the operating system and hypervisor. Vulnerabilities enabling SMM code execution are often reported as Common Vulnerabilities and Exposures (CVEs); however, no security mechanisms currently exist to prevent attackers from analyzing those vulnerabilities. To increase the cost of vulnerability analysis of SMM modules, we introduced SmmPack. The core concept of SmmPack involves encrypting an SMM module with the key securely stored in a Trusted Platform Module (TPM). We assessed the effectiveness of SmmPack in preventing attackers from obtaining and analyzing SMM modules using various acquisition methods. Our results show that SmmPack significantly increases the cost by narrowing down the means of module acquisition. Furthermore, we demonstrated that SmmPack operates without compromising the performance of the original SMM modules. We also clarified the management and adoption methods of SmmPack, as well as the procedure for applying BIOS updates, and demonstrated that the implementation of SmmPack is realistic.

cs.CR↗

arXiv2023

Revisitation of the lock-in transition in one-dimensional charge-density waves

We studied the lock-in transition of charge-density waves of one-dimensional conductors. Though this phenomenon has been known for decades, there are still discrepancies between the theories and the experiments. We focused on the pioneering study of this phenomenon by McMillan and revisited, in particular, his numerical calculations. We first reproduced his results by providing unwritten information in the article. The obtained critical point was in good agreement with the previous study, as well as the analytical solution proposed later. We found a simple power-law behavior of the free energy in the critical regime, leading to the power-law divergence of the specific heat. We also introduced the concept of stiffness, equivalent to helicity modulus, which also showed a power-law behavior. These results allowed us to propose a new perspective on the lock-in transition.

cond-mat.str-el↗

arXiv2022

Conformality of Charge Density Wave

New quantum phenomena are continuously being discovered in 2D systems. In particular, the charge density wave (CDW) has the aspect of a quantum crystal with a macroscopic wave function (order parameter), so unlike quantum liquids (superconductivity, quantum Hall liquids $^3$He, $^4$He), new ground states such as supersolid and Moir\'e solids can be expected. However, it is difficult to describe these states because of their quantum aspect, hence there is still no theory that can explain CDW phases in a unified way. The best way to describe a quantum crystal seems to be a conformal transformation that allows local deformation (wave properties) and preserves local angles (crystal properties). Here, we propose a unifying conformal description of 2D CDW phases in the typical 2D CDW material transition metal dichalcogenides (MX$_2$). We discover that the discommensurate CDW phases in MX$_2$ can be explained beautifully by a discrete conformal transformation of CDW wavevectors. This conformality is due to commensurability of CDW with the MX$_2$ lattice. In other words, interference of harmonic wavefunction induces conformality. Using this new conformal formulation, we explain experimental nearly-commensurate/stripe/T CDW phases in 1$T$-TaS$_2$ ($\sqrt{13}\times\sqrt{13}$ structure), 2$H$-TaSe$_2$ ($\sqrt{9}\times\sqrt{9}$ structure), and explain the origin of a new experimental nearly-commensurate phase in TaSe$_2$ thin-film ($\sqrt{7}\times\sqrt{7}$ structure). This theory is very simple in the sense that it includes only discommensuration and comprises physics as rich as quantum Hall liquids. This new description will broaden our perspective of quantum crystals.

cond-mat.str-el↗

arXiv2020

Visualization of the strain-induced topological phase transition in a quasi-one-dimensional superconductor TaSe3

Control of the phase transition from topological to normal insulators can allow for an on/off switching of spin current. While topological phase transitions have been realized by elemental substitution in semiconducting alloys, such an approach requires the preparation of materials with various compositions, thus it is quite far from a feasible device application, which demands a reversible operation. Here we use angle-resolved photoemission spectroscopy (ARPES) and spin-resolved ARPES to visualize the strain-driven band structure evolution of the quasi-1D superconductor TaSe3. We demonstrate that it undergoes reversible strain-induced topological phase transitions from a strong topological insulator phase with spin-polarized, quasi-1D topological surface states, to topologically trivial semimetal and band insulating phases. The quasi-1D superconductor TaSe3 provides a suitable platform for engineering the topological spintronics, for example as an on/off switch for spin current robust against impurity scattering.

cond-mat.mtrl-sci↗

arXiv2020

The Nakano-Nishijima-Gell-Mann Formula From Discrete Galois Fields

The well known Nakano-Nishijima-Gell-Mann (NNG) formula relates certain quantum numbers of elementary particles to their charge number. This equation, which phenomenologically introduces the quantum numbers $I_z$ (isospin), $S$ (strangeness), etc., is constructed using group theory with real numbers $\mathbb{R}$. But, using a discrete Galois field $\mathbb{F}_p$ instead of $\mathbb{R}$ and assuring the fundamental invariance laws such as unitarity, Lorentz invariance, and gauge invariance, we derive the NNG formula deductively from Meson (two quarks) and Baryon (three quarks) representations in a unified way. Moreover, we show that quark confinement ascribes to the inevitable fractionality caused by coprimeness between half-integer (1/2) of isospin and number of composite particles (e.g. three).

hep-ph↗

arXiv2019

Origin of Stripe and Quasi-Stripe CDW Structures in Monolayer MX$ _2$ compounds: Multivalley Free Energy Landscape

Ultrathin sheets of transition metal dichalcogenides (MX$ _2$) with charge density waves (CDWs) is increasingly gaining interest as a promising candidate for graphene-like devices. Although experimental data including stripe/quasi-stripe structure and hidden states have been reported, the ground state of ultrathin MX$ _2$ compounds and, in particular, the origin of anisotropic (stripe and quasi-stripe) CDW phases is a long-standing problem. Anisotropic CDW phases have been explained by Coulomb interaction between domain walls and inter-layer interaction. However, these models assume that anisotropic domain walls can exist in the first place. Here, we report that anisotropic CDW domain walls can appear naturally without assuming anisotropic interactions: We explain the origin of these phases by topological defect theory (line defects in a two-dimensional plane) and interference between harmonics of macroscopic CDW wave functions. We revisit the McMillan-Nakanishi-Shiba model for monolayer 1$T$-TaS$ _2$ and 2$H$-TaSe$ _2$ and show that CDWs with wave vectors that are separated by $120^\circ$ (i.e. the three-fold rotation symmetry of the underlying lattice) contain a free-energy landscape with many local minima. Then, we remove this $120^\circ$ constraint and show that free energy local minima corresponding to the stripe and quasi-stripe phase appear. Our results imply that Coulomb interaction between domain walls and inter-layer interaction may be secondary factors for the appearance of these phases. Furthermore, this model can predict new CDW phases, hence it may become the basis to study CDW further. We anticipate our results to be a starting point for further study in two-dimensional physics, such as explanation of "Hidden CDW states", study the interplay between supersolid symmetry and lattice symmetry, and application to other van der Waals structures.

cond-mat.mtrl-sci↗

arXiv2019

Effect of Cu intercalation and pressure on excitonic interaction in 1T-TiSe2

1T-TiSe2 has a semimetallic band structure at room temperature and undergoes phase transition to a triple-q charge density wave (CDW) state with a commensurate superlattice structure (2a * 2a * 2c) below Tc ~ 200 K at ambient pressure. This phase transition is caused by cooperative phenomena involving electron-phonon and electron-hole (excitonic) interactions, and cannot be described by a standard CDW framework. By Cu intercalation or the application of pressure, this phase transition temperature is suppressed and superconductivity (SC) appears. However, it is not clear what kind of order parameters are affected by these two procedures. We investigated the crystal structure of CuxTiSe2 and pressurized 1T-TiSe2 around the SC state by synchrotron x-ray diffraction on single crystals. In the high-temperature phase, the variation of structural parameters for the case of Cu intercalation and application of pressure are considerably different. Moreover, the relationship between the critical points of the CDW phase transition and the SC dome are also different for the two cases. The excitonic interaction appears to play an important role in the P-T phase diagram of 1T-TiSe2, but not in the x-T phase diagram.

cond-mat.str-el↗

arXiv2018

Effect of Cu doping on superconductivity in TaSe$_3$: Relationship between superconductivity and induced charge density wave

By measuring the temperature dependence of the resistance, we investigated the effect of Cu doping on superconductivity (SC) in Cu-doped TaSe$_3$ in which the charge density wave (CDW) transition is induced by Cu doping. We observed an emergence of a region where the SC transition temperature ($T_\mathrm{C}$) decreased in samples with higher Cu concentrations and found that the region tended to expand with increasing Cu concentration. In addition, the temperature dependence of the upper critical field ($H_\mathrm{C2}$) of Cu-doped TaSe$_3$ was found to differ from that of pure TaSe$_3$. Based on these experimental results and the fact that the SC of TaSe$_3$ is filamentary, we conclude that SC is suppressed locally by Cu doping and competes with the CDW in Cu-doped TaSe$_3$. The resistance anomaly due to the CDW transition was extremely small and the size of the anomaly was enhanced with increasing Cu concentration but the temperature at which the anomaly appeared hardly changed. This result of the anomaly and the local suppression of SC imply that the induced CDWs are short-range order in the vicinity of Cu atoms. We also discuss the effect of the pinning of CDWs on the relationship between SC and short-range order CDWs.

cond-mat.supr-con↗

arXiv2017

Lock-in transition of charge density waves in quasi-one-dimensional conductors: reinterpretation of McMillan's theory

We investigated the lock-in transition of charge density waves (CDWs) in quasi-one-dimensional conductors, based on McMillan's free energy. The higher-order umklapp terms play an essential role in this study. McMillan's theory was extended by Nakanishi and Shiba in order to treat multiple CDW vectors. Although their theories were aimed at understanding CDWs in quasi-two-dimensional conductors, we applied them to the quasi-one-dimensional conductors, including K$_{0.3}$MoO$_3$, NbSe$_3$, and $m$-TaS$_3$, and confirmed its validity for these cases. Then we discussed our previous experimental result of $o$-TaS$_3$, which revealed the coexistence of commensurate and incommensurate states. We found that the coexistence of multiple CDW vectors is essential for the lock-in transition to occur in $o$-TaS$_3$. The even- and odd-order terms in the free energy play roles for amplitude development and phase modulation, respectively. Moreover, consideration of the condition of being commensurate CDWs allowed us to relate it with that of the weak localization in random media.

cond-mat.str-el↗

arXiv2017

Detect Kernel-Mode Rootkits via Real Time Logging & Controlling Memory Access

Modern malware and spyware platforms attack existing antivirus solutions and even Microsoft PatchGuard. To protect users and business systems new technologies developed by Intel and AMD CPUs may be applied. To deal with the new malware we propose monitoring and controlling access to the memory in real time using Intel VT-x with EPT. We have checked this concept by developing MemoryMonRWX, which is a bare-metal hypervisor. MemoryMonRWX is able to track and trap all types of memory access: read, write, and execute. MemoryMonRWX also has the following competitive advantages: fine-grained analysis, support of multi-core CPUs and 64-bit Windows 10. MemoryMonRWX is able to protect critical kernel memory areas even when PatchGuard has been disabled by malware. Its main innovative features are as follows: guaranteed interception of every memory access, resilience, and low performance degradation.

cs.CR↗

arXiv2017

Direct Observation of Mono-, Bi-, and Tri-layer Charge Density Waves in 1T-TaS_2 by Transmission Electron Microscopy without a Substrate

Charge-density-waves (CDW) which occur mainly in low-dimensional systems have a macroscopic wave function similar to superfluids and superconductors. Kosterlitz-Thouless (KT) transition is observed in superfluids and superconductors, but the presence of KT transition in ultra-thin CDW systems has been an open problem. We report the direct real-space observation of CDWs with new order states in mono-, bi-, and tri-layer 1T-TaS_2 crystal by using a low voltage scanning-transmission-electron-microscope (STEM) without a substrate. This method is ideal to observe local atomic structures and possible defects. We clearly observed that the mono-layer crystal has a new triclinic stripe CDW order without the triple q condition q_1 + q_2 + q_3 = 0. A strong electron-phonon interaction gives rise to new crevasse (line) type defects instead of disclination (point) type defects due to the KT transition. These results reaffirm the importance of the electron-phonon interaction in mono-layer nanophysics.

cond-mat.mtrl-sci↗

arXiv2017

Co-appearance of superconductivity and ferromagnetism in a Ca$_2$RuO$_4$ nanofilm crystal

By tuning the physical and chemical pressures of layered perovskite materials we can realize the quantum states of both superconductors and insulators. By reducing the thickness of a layered crystal to a nanometer level, a nanofilm crystal can provide novel quantum states that have not previously been found in bulk crystals. Here we report the realization of high-temperature superconductivity in Ca$_2$RuO$_4$ nanofilm single crystals. Ca$_2$RuO$_4$ thin film with the highest transition temperature $T_c$ (midpoint) of 64~K exhibits zero resistance in electric transport measurements. The superconducting critical current exhibited a logarithmic dependence on temperature and was enhanced by an external magnetic field. Magnetic measurements revealed a ferromagnetic transition at 180~K and diamagnetic magnetization due to superconductivity. Our results suggest the co-appearance of superconductivity and ferromagnetism in Ca$_2$RuO$_4$ nanofilm crystals. We also found that the induced bias current and the tuned film thickness caused a superconductor-insulator transition. The fabrication of micro-nanocrystals made of layered material enables us to discuss rich superconducting phenomena in ruthenates.

cond-mat.supr-con↗

arXiv2017

Quantum Time Crystal By Decoherence: Proposal With Incommensurate Charge Density Wave Ring

We show that time translation symmetry of a ring system with a macroscopic quantum ground state is broken by decoherence. In particular, we consider a ring-shaped incommensurate charge density wave (ICDW ring) threaded by a fluctuating magnetic flux: the Caldeira-Leggett model is used to model the fluctuating flux as a bath of harmonic oscillators. We show that the charge density expectation value of a quantized ICDW ring coupled to its environment oscillates periodically. The Hamiltonians considered in this model are time independent unlike "Floquet time crystals" considered recently. Our model forms a metastable quantum time crystal with a finite length in space and in time.

quant-ph↗

arXiv2016

Chiral Unitary Quantum Phase Transition in 2H-Fe$_x$TaSe$_2$

We have observed a metal-insulator transition of a quasi-two dimensional electronic system in transition metal dichalcogenide $2H$-TaSe$_2$ caused by doping iron. The sheet resistance of $2H$-Fe$_x$TaSe$_2$ ($0 \leq x \leq 0.120$) single crystals rises about $10^6$ times with the increasing of $x$ at the lowest temperature. We investigated the temperature dependence of the resistance and found a metal-insulator transition with a critical sheet resistance $11.7 \pm 5.4$ k$\rm{\Omega}$. The critical exponent of the localization length $\nu$ is estimated $0.31 \pm 0.18$. The values of the critical sheet resistance and $\nu$ are accordant to those of the \textit{chiral unitary class} (less than $h/1.49e^2=17.3$ k$\rm{\Omega}$ and $0.35 \pm 0.03$, respectively). We suggest that $2H$-Fe$_x$TaSe$_2$ is classified as the chiral unitary class, not as standard unitary class.

cond-mat.mes-hall↗