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Phonon-modulated Kerr nonlinearity in ultrathin 2H-MoTe2
Authors:
Shaoxiang Sheng,
Yang Luo,
Chenyu Wang,
Sayooj Sateesh,
Yaxian Wang,
Marko Burghard,
Sayantan Patra,
Bhumika Chauhan,
Ashish Arora,
Sheng Meng,
Manish Garg
Abstract:
Controlling nonequilibrium responses in optically driven quantum materials is essential for advancing applications in energy conversion, ultrafast electronics, and quantum computation. Nonlinear optical spectroscopy serves as a powerful tool to investigate ultrafast electron and phonon dynamics in these systems; however, conventional nonlinear approaches often require intense laser pulses (> 10 GW…
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Controlling nonequilibrium responses in optically driven quantum materials is essential for advancing applications in energy conversion, ultrafast electronics, and quantum computation. Nonlinear optical spectroscopy serves as a powerful tool to investigate ultrafast electron and phonon dynamics in these systems; however, conventional nonlinear approaches often require intense laser pulses (> 10 GW/cm2) and typically encounter a strong background. Here, we introduce a phase-sensitive nonlinear spectroscopic technique that operates at low laser powers (~ 10 kW/cm2, pulse energies ~ 10 pJ) and enables real-time monitoring and active control of coherent phonons in a few-layer (three to five) thick 2H-MoTe2. Upon excitation with ultrashort (~ 10 fs) pump pulses, we achieve displacive excitation of coherent phonons, which periodically modulate the Kerr nonlinearity of the material, leading to cross-phase modulation (XPM) of a delayed probe pulse. This phase modulation induces spectral broadening and oscillations in the center of mass (COM) of the probe spectrum in time, enabling the detection of subtle nonlinear optical responses in a background-free manner. The nonlinear response can be selectively amplified or attenuated by adjusting the strength of the pump pulse, which controls the distribution of photoexcited carriers in the electronic bands. By combining two-color nondegenerate pump-probe measurements and time-dependent density-functional theory (TDDFT) calculations, we directly resolve the coupled nonequilibrium electronic and phonon dynamics. A dual-pump pulse scheme enables precise control of phonon oscillations, allowing selective activation or suppression of specific phonon modes and correspondingly the modulation of the Kerr nonlinearity.
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Submitted 19 March, 2026;
originally announced March 2026.
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Unexpectedly super strong paramagnetism of aromatic peptides due to cations of divalent metals
Authors:
Haijun Yang,
Liuhua Mu,
Lei Zhang,
Zixin Wang,
Shiqi Sheng,
Yongshun Song,
Peng Xiu,
Jihong Wang,
Guosheng Shi,
Jun Hu,
Xin Zhang,
Feng Zhang,
Haiping Fang
Abstract:
The magnetism of most biological systems has not been characterized, which directly impedes our understanding of many magnetic field-related phenomena, including magnetoreception and magnetic bio-effects. Here we measured the magnetic susceptibility of aromatic peptide AYFFF self-assemblies in the presence or absence of divalent metal cations in liquid phase at room temperature. Unexpectedly, the…
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The magnetism of most biological systems has not been characterized, which directly impedes our understanding of many magnetic field-related phenomena, including magnetoreception and magnetic bio-effects. Here we measured the magnetic susceptibility of aromatic peptide AYFFF self-assemblies in the presence or absence of divalent metal cations in liquid phase at room temperature. Unexpectedly, the magnetic susceptibilities of AYFFF self-assemblies in the chloride solution of various divalent cations (Mg2+, Zn2+, and Cu2+) show super strong paramagnetism. We attribute the super strong paramagnetism to existence of the magnetic moments on the cations adsorbed on aromatic rings in the AYFFF assemblies through hydrated cation-π interactions, where the adsorbed cations display non-divalent behavior with unpaired electron spins. Our results indicate the super strong paramagnetism or potential ferromagnetism in the aromatic ring-enriched biomolecules when there are enough cations of divalent metals adsorbed. The findings not only provide fundamental information for understanding the magnetism of biological systems, provoke insights for investigating the origin of magnetoreception and bio-effects of magnetic fields, but also help developing future magnetic-control techniques on aromatic ring-enriched biomolecules and drugs in living organisms, as well as biomaterial fabrication and manipulation.
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Submitted 9 December, 2020; v1 submitted 24 November, 2020;
originally announced November 2020.
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Thermodynamics of majority-logic decoding in information erasure
Authors:
Shiqi Sheng,
Tim Herpich,
Giovanni Diana,
Massimiliano Esposito
Abstract:
We investigate the performance of majority-logic decoding in both reversible and finite-time information erasure processes performed on macroscopic bits that contain $N$ microscopic binary units. While we show that for reversible erasure protocols single-unit transformations are more efficient than majority-logic decoding, the latter is found to offer several benefits for finite-time erasure proce…
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We investigate the performance of majority-logic decoding in both reversible and finite-time information erasure processes performed on macroscopic bits that contain $N$ microscopic binary units. While we show that for reversible erasure protocols single-unit transformations are more efficient than majority-logic decoding, the latter is found to offer several benefits for finite-time erasure processes: Both the minimal erasure duration for a given erasure and the minimal erasure error for a given erasure duration are reduced, if compared to a single unit. Remarkably, the majority-logic decoding is also more efficient in both the small erasure error and fast erasure region. These benefits are also preserved under the optimal erasure protocol that minimizes the dissipated heat. Our work therefore shows that majority-logic decoding can lift the precision-speed-efficiency trade-off in information erasure processes.
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Submitted 15 March, 2019; v1 submitted 10 January, 2019;
originally announced January 2019.
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Experimental realization of graphene-like borophene
Authors:
Wenbin Li,
Longjuan Kong,
Caiyun Chen,
Jian Gou,
Shaoxiang Sheng,
Weifeng Zhang,
Hui Li,
Lan Chen,
Peng Cheng,
Kehui Wu
Abstract:
We report a successful preparation of a purely honeycomb, graphene-like borophene, by using an Al(111) surface as the substrate and molecular beam epitaxy (MBE) growth in ultrahigh vacuum. Our scanning tunneling microscopy (STM) reveals perfect monolayer borophene with planar, non-buckled honeycomb lattice similar as graphene. Theoretical calculations show that the honeycomb borophene on Al(111) i…
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We report a successful preparation of a purely honeycomb, graphene-like borophene, by using an Al(111) surface as the substrate and molecular beam epitaxy (MBE) growth in ultrahigh vacuum. Our scanning tunneling microscopy (STM) reveals perfect monolayer borophene with planar, non-buckled honeycomb lattice similar as graphene. Theoretical calculations show that the honeycomb borophene on Al(111) is energetically stable. Remarkably, nearly one electron charge is transferred to each boron atom from the Al(111) substrate and stabilizes the honeycomb borophene structure, in contrast to the little charge transfer in borophene/Ag(111) case. This work demonstrates that the borophene lattice can be manipulated by controlling the charge transfer between the substrate and the borophene film.
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Submitted 23 December, 2017;
originally announced December 2017.
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Direct evidences of pentagonal silicon chains and magic clusters
Authors:
Shaoxiang Sheng,
Runze Ma,
Jiangbin Wu,
Wenbin Li,
Longjuan Kong,
Xin Cong,
Duanyun Cao,
Wenqi Hu,
Jun-Wei Luo,
Peng Cheng,
Ping-Heng Tan,
Ying Jiang,
Lan Chen,
Kehui Wu
Abstract:
Pentagon is one of the most beautiful geometric structures in nature, but it is rarely seen simply because five-fold symmetry is mathematically forbidden in a 2D or 3D periodic lattices. Fortunately, pentagon as a structural element is allowed in 1D or 0D systems, since translational symmetry is not necessary there. However, in these systems pentagons only compose a small portion of the structure.…
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Pentagon is one of the most beautiful geometric structures in nature, but it is rarely seen simply because five-fold symmetry is mathematically forbidden in a 2D or 3D periodic lattices. Fortunately, pentagon as a structural element is allowed in 1D or 0D systems, since translational symmetry is not necessary there. However, in these systems pentagons only compose a small portion of the structure. So far, 1D or 0D systems consisting of purely pentagons are still rare. Here, combing high resolution non-contact atomic force microscopy and tip-enhanced Raman spectroscopy, we have directly visualized the pentagon-ring structure in self-assembled Si nanoribbons and magic clusters on Ag(110) substrate. Moreover, chemical fingerprint of Si pentagon was detected in individual Si nanoribbon and clusters by tip-enhanced Raman spectroscopy. This work demonstrates that Si pentagon can be an important element in building silicon nanostructures, which may find potential applications in future nanoelectronics based on silicon.
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Submitted 25 November, 2017;
originally announced November 2017.
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Synthesis of Borophene Nanoribbons on Ag(110) Surface
Authors:
Qing Zhong,
Longjuan Kong,
Jian Gou,
Wenbin Li,
Shaoxiang Sheng,
Shuo Yang,
Peng Cheng,
Hui Li,
Kehui Wu,
Lan Chen
Abstract:
We present the successful synthesis of single-atom-thick borophene nanoribbons (BNRs) by self-assembly of boron on Ag(110) surface. The scanning tunneling microscopy (STM) studies reveal high quality BNRs: all the ribbons are along the [-110] direction of Ag(110), and can run across the steps on the surface. The width of ribbons is distributed in a narrow range around 10.3 nm. High resolution STM…
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We present the successful synthesis of single-atom-thick borophene nanoribbons (BNRs) by self-assembly of boron on Ag(110) surface. The scanning tunneling microscopy (STM) studies reveal high quality BNRs: all the ribbons are along the [-110] direction of Ag(110), and can run across the steps on the surface. The width of ribbons is distributed in a narrow range around 10.3 nm. High resolution STM images revealed four ordered surface structures in BNRs. Combined with DFT calculations, we found that all the four structures of boron nanoribbons consist of the boron chains with different width, separated by hexagonal hole arrays. The successful synthesis of BNRs enriches the low dimensional allotrope of boron and may promote further applications of borophene
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Submitted 18 April, 2017;
originally announced April 2017.
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Hidden symmetries and nonlinear constitutive relations for tight-coupling heat engines
Authors:
Shiqi Sheng,
Z. C. Tu
Abstract:
Typical heat engines exhibit a kind of homotypy: The heat exchanges between a cyclic heat engine and its two heat reservoirs abide by the same function type; the forward and backward flows of an autonomous heat engine also conform to the same function type. This homotypy mathematically reflects in the existence of hidden symmetries for heat engines. The heat exchanges between the cyclic heat engin…
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Typical heat engines exhibit a kind of homotypy: The heat exchanges between a cyclic heat engine and its two heat reservoirs abide by the same function type; the forward and backward flows of an autonomous heat engine also conform to the same function type. This homotypy mathematically reflects in the existence of hidden symmetries for heat engines. The heat exchanges between the cyclic heat engine and its two reservoirs are dual under the joint transformation of parity inversion and time-reversal operation. Similarly, the forward and backward flows in the autonomous heat engine are also dual under the parity inversion. With the consideration of these hidden symmetries, we derive a generic nonlinear constitutive relation up to the quadratic order for tight-coupling cyclic heat engines and that for tight-coupling autonomous heat engines, respectively.
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Submitted 19 January, 2015; v1 submitted 14 January, 2015;
originally announced January 2015.
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Constitutive Relation for Nonlinear Response and Universality of Efficiency at Maximum Power for Tight-Coupling Heat Engines
Authors:
Shiqi Sheng,
Z. C. Tu
Abstract:
We present a unified perspective on nonequilibrium heat engines by generalizing nonlinear irreversible thermodynamics. For tight-coupling heat engines, a generic constitutive relation of nonlinear response accurate up to the quadratic order is derived from the symmetry argument and the stall condition. By applying this generic nonlinear constitutive relation to finite-time thermodynamics, we obtai…
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We present a unified perspective on nonequilibrium heat engines by generalizing nonlinear irreversible thermodynamics. For tight-coupling heat engines, a generic constitutive relation of nonlinear response accurate up to the quadratic order is derived from the symmetry argument and the stall condition. By applying this generic nonlinear constitutive relation to finite-time thermodynamics, we obtain the necessary and sufficient condition for the universality of efficiency at maximum power, which states that a tight-coupling heat engine takes the universal efficiency at maximum power up to the quadratic order if and only if either the engine symmetrically interacts with two heat reservoirs or the elementary thermal energy flowing through the engine matches the characteristic energy of the engine. As a result, we solve the following paradox: On the one hand, the universal quadratic term in the efficiency at maximum power for tight-coupling heat engines proved as a consequence of symmetry [M. Esposito, K. Lindenberg, and C. Van den Broeck, Phys. Rev. Lett. 102, 130602 (2009); S. Q. Sheng and Z. C. Tu, Phys. Rev. E 89, 012129 (2014)]; On the other hand, two typical heat engines including the Curzon-Ahlborn endoreversible heat engine [F. L. Curzon and B. Ahlborn, Am. J. Phys. 43, 22 (1975)] and the Feynman ratchet [Z. C. Tu, J. Phys. A 41, 312003 (2008)] recover the universal efficiency at maximum power regardless of any symmetry.
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Submitted 17 January, 2015; v1 submitted 28 April, 2014;
originally announced April 2014.
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Coefficient of performance at maximum χ-criterion for Feynman ratchet as a refrigerator
Authors:
Shiqi Sheng,
Pan Yang,
Z. C. Tu
Abstract:
The χ-criterion is defined as the product of the energy conversion efficiency and the heat absorbed per-unit-time by the working substance [de Tomás et al., Phys. Rev. E, 85 (2012) 010104(R)]. The χ-criterion for Feynman ratchet as a refrigerator operating between two heat baths is optimized. Asymptotic solutions of the coefficient of performance at maximum χ-criterion for Feynman ratchet are inve…
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The χ-criterion is defined as the product of the energy conversion efficiency and the heat absorbed per-unit-time by the working substance [de Tomás et al., Phys. Rev. E, 85 (2012) 010104(R)]. The χ-criterion for Feynman ratchet as a refrigerator operating between two heat baths is optimized. Asymptotic solutions of the coefficient of performance at maximum χ-criterion for Feynman ratchet are investigated at both large and small temperature difference. An interpolation formula, which fits the numerical solution very well, is proposed. Besides, the sufficient condition for the universality of the coefficient of performance at maximum χis investigated.
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Submitted 27 February, 2014; v1 submitted 26 February, 2014;
originally announced February 2014.
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Weighted reciprocal of temperature, weighted thermal flux, and their applications in finite-time thermodynamics
Authors:
Shiqi Sheng,
Z. C. Tu
Abstract:
The concepts of weighted reciprocal of temperature and weighted thermal flux are proposed for a heat engine operating between two heat baths and outputting mechanical work. With the aid of these two concepts, the generalized thermodynamic fluxes and forces can be expressed in a consistent way within the framework of irreversible thermodynamics. Then the efficiency at maximum power output for a hea…
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The concepts of weighted reciprocal of temperature and weighted thermal flux are proposed for a heat engine operating between two heat baths and outputting mechanical work. With the aid of these two concepts, the generalized thermodynamic fluxes and forces can be expressed in a consistent way within the framework of irreversible thermodynamics. Then the efficiency at maximum power output for a heat engine, one of key topics in finite-time thermodynamics, is investigated on the basis of a generic model under the tight-coupling condition. The corresponding results have the same forms as those of low-dissipation heat engines [M. Esposito, R. Kawai, K. Lindenberg, and C. Van den Broeck, {Phys. Rev. Lett.} \textbf{105}, 150603 (2010)]. The mappings from two kinds of typical heat engines, such as the low-dissipation heat engine and the Feynman ratchet, into the present generic model are constructed. The universal efficiency at maximum power output up to the quadratic order is found to be valid for a heat engine coupled symmetrically and tightly with two baths. The concepts of weighted reciprocal of temperature and weighted thermal flux are also transplanted to the optimization of refrigerators.
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Submitted 22 January, 2014; v1 submitted 11 September, 2013;
originally announced September 2013.
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Large and temperature-independent piezoelectric response in Pb(Mg1/3Nb2/3)O3-BaTiO3-PbTiO3
Authors:
Lizhu Huang,
Guorong Li,
Desheng Fu,
Suzie Sheng,
Jiangtao Zeng,
Huarong Zeng
Abstract:
The temperature dependence of elastic, dielectric, and piezoelectric properties of (65-x)Pb(Mg1/3Nb2/3)O3-xBaTiO335-PbTiO3 ceramics with x=0, 1, 2, 3, and 4 was investigated. Compound with x=2 was found to exhibit a large piezoelectric response (d31=-170 pC/N, d33=530 pC/N at 300 K). Particularly, its d31 value was nearly a constant over a temperature range from 185 to 360 K. A broad ferroelectric…
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The temperature dependence of elastic, dielectric, and piezoelectric properties of (65-x)Pb(Mg1/3Nb2/3)O3-xBaTiO335-PbTiO3 ceramics with x=0, 1, 2, 3, and 4 was investigated. Compound with x=2 was found to exhibit a large piezoelectric response (d31=-170 pC/N, d33=530 pC/N at 300 K). Particularly, its d31 value was nearly a constant over a temperature range from 185 to 360 K. A broad ferroelectric phase transition tuned by BaTiO3 doping was deduced from the dielectric constant, elastic compliance constant and Raman spectra. The temperature-stable piezoelectric response was attributed to the counter-balance of contributions from the dielectric and elastic responses.
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Submitted 16 January, 2013;
originally announced January 2013.
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Universality of energy conversion efficiency for optimal tight-coupling heat engines and refrigerators
Authors:
Shiqi Sheng,
Z. C. Tu
Abstract:
A unified $χ$-criterion for heat devices (including heat engines and refrigerators) which is defined as the product of the energy conversion efficiency and the heat absorbed per unit time by the working substance [de Tomás \emph{et al} 2012 \textit{Phys. Rev. E} \textbf{85} 010104(R)] is optimized for tight-coupling heat engines and refrigerators operating between two heat baths at temperatures…
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A unified $χ$-criterion for heat devices (including heat engines and refrigerators) which is defined as the product of the energy conversion efficiency and the heat absorbed per unit time by the working substance [de Tomás \emph{et al} 2012 \textit{Phys. Rev. E} \textbf{85} 010104(R)] is optimized for tight-coupling heat engines and refrigerators operating between two heat baths at temperatures $T_c$ and $T_h(>T_c)$. By taking a new convention on the thermodynamic flux related to the heat transfer between two baths, we find that for a refrigerator tightly and symmetrically coupled with two heat baths, the coefficient of performance (i.e., the energy conversion efficiency of refrigerators) at maximum $χ$ asymptotically approaches to $\sqrt{\varepsilon_C}$ when the relative temperature difference between two heat baths $\varepsilon_C^{-1}\equiv (T_h-T_c)/T_c$ is sufficiently small. Correspondingly, the efficiency at maximum $χ$ (equivalent to maximum power) for a heat engine tightly and symmetrically coupled with two heat baths is proved to be $η_C/2+η_C^2/8$ up to the second order term of $η_C\equiv (T_h-T_c)/T_h$, which reverts to the universal efficiency at maximum power for tight-coupling heat engines operating between two heat baths at small temperature difference in the presence of left-right symmetry [Esposito \emph{et al} 2009 \textit{Phys. Rev. Lett.} \textbf{102} 130602].
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Submitted 25 May, 2013; v1 submitted 31 December, 2012;
originally announced December 2012.
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Spin states and persistent currents in a mesoscopic ring with an embedded magnetic impurity
Authors:
J. S. Sheng,
Kai Chang
Abstract:
Spin states and persistent currents are investigated theoretically in a mesoscopic ring with an embedded magnetic ion under a uniform magnetic field including the spin-orbit interactions. The magnetic impurity acts as a spin-dependent $δ$-potential for electrons and results in gaps in the energy spectrum, consequently suppresses the oscillation of the persistent currents. The competition between…
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Spin states and persistent currents are investigated theoretically in a mesoscopic ring with an embedded magnetic ion under a uniform magnetic field including the spin-orbit interactions. The magnetic impurity acts as a spin-dependent $δ$-potential for electrons and results in gaps in the energy spectrum, consequently suppresses the oscillation of the persistent currents. The competition between the Zeeman splittings and the $s$-$d$ exchange interaction leads to a transition of the electron ground state in the ring. The interplay between the periodic potential induced by the Rashba and Dresselhaus spin-orbit interactions and the $δ$-potential induced by the magnetic impurity leads to significant variation in the energy spectrum, charge density distribution, and persistent currents of electrons in the ring.
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Submitted 26 June, 2007;
originally announced June 2007.
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Spin states and persistent currents in mesoscopic rings: spin-orbit interactions
Authors:
J. S. Sheng,
Kai Chang
Abstract:
We investigate theoretically electron spin states in one dimensional (1D) and two dimensional (2D) hard-wall mesoscopic rings in the presence of both the Rashba spin-orbit interaction (RSOI) and the Dresselhaus spin-orbit interaction (DSOI) in a perpendicular magnetic field. The Hamiltonian of the RSOI alone is mathematically equivalent to that of the DSOI alone using an SU(2) spin rotation tran…
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We investigate theoretically electron spin states in one dimensional (1D) and two dimensional (2D) hard-wall mesoscopic rings in the presence of both the Rashba spin-orbit interaction (RSOI) and the Dresselhaus spin-orbit interaction (DSOI) in a perpendicular magnetic field. The Hamiltonian of the RSOI alone is mathematically equivalent to that of the DSOI alone using an SU(2) spin rotation transformation. Our theoretical results show that the interplay between the RSOI and DSOI results in an effective periodic potential, which consequently leads to gaps in the energy spectrum. This periodic potential also weakens and smoothens the oscillations of the persistent charge current (CC) and spin current (SC) and results in the localization of electrons. For a 2D ring with a finite width, higher radial modes destroy the periodic oscillations of persistent currents.
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Submitted 12 October, 2006; v1 submitted 7 September, 2006;
originally announced September 2006.