The 45 K Onset Superconductivity and the Suppression of the Nematic Order in FeSe by Electrolyte Gating

The electronic doping effect on both the superconductivity and the nematic order in the FeSe nanoflake are investigated by using the electric-double-layer transistor configuration. The superconductivity can be effectively controlled by electronic doping, and the onset superconducting transition temperature Tc reaches as high as 45 K at a gate voltage Of Vg = 4 V. Meanwhile, the nematic phase is gradually suppressed with the increase of electronic doping （or Vg）. The results provide an effective method with variable charge doping for investigation of the rich physics in the FeSe superconductor.

Frustrated superconductivity and sextetting order

The superconducting state typically favors a uniform spatial distribution akin to ferromagnetism.Nevertheless,the pair-densitywave state exhibits sign changes in the pairing order,leading to potential frustrations in phase coherence.We propose a mechanism to the sextetting order stemming from the frustrations in the phase coherence of a pair-density-wave state,whose spatial modulation manifests a vortex-antivortex honeycomb lattice.The classical ground state configurations are mapped to Baxter's three-coloring model,revealing a macroscopic degeneracy accompanied by extensive entropy.The phase coherence problem intertwines the U(1)phases and the vorticity variables.While the resultant color and phase fluctuations suppress the pair-densitywave order,they maintain the sextetting order above the superconducting transition temperature(T_(c)).The 1/3-fractional vortex emerges as the fundamental topological defect in the sextetting order.This novel mechanism of frustrated superconductivity provides an alternative explanation for the experimental observed fractional oscillations in CsV_(3)Sb_(5).

Coexistence of Superconductivity and Antiferromagnetism in SmAsO1-xFxFe

Superconductivity and magnetism have been interesting topics in condensed mater physics and they have been studied experimentally and theoretically for many years. These two cooperative phenomena are antagonistic until the discovery of some rare earth ternary compounds that show the coexistence of superconductivity and magnetism. In some of the recently discovered iron-based layered superconductors, superconductivity and magnetism coexist. In the present work we examine the possibility of coexistence of antiferromagnetism and superconductivity in samarium arsenide oxide superconductor (SmAsO1-xFxFe). Using a model of the Hamiltonian and retarded double time Greens function formalism, we found expressions AFM order Parameter (η) and AFM transition temperature (Tm). We obtained the phase diagrams (Tc vs η) and(Tm vs η) to obtain the region where orders, i.e., superconductivity and AFM (antiferromagnetism), coexisted. The region under the intersection of the two merged graphs shows that superconductivity and AFM coexist in the system (SmAsO1-xFxFe).

Unconventional chiral d-wave superconducting state in strained graphene

We consider a highly unconventional superconducting state with chiral d-wave symmetry in doped graphene under strain with the Gutzwiller–RVB method in the momentum space. It is shown that flat bands emerge in the normal state for reasonable strain. As a result, the superconducting critical temperature is found to be linearly proportional to the strength of the electron–electron interaction. Furthermore, the chiral d-wave superconducting state is shown with coexistence of the charge density wave and the pair density wave. There are different coexisting states with those orders under different doping levels.

Multiband nodeless superconductivity near the charge-density-wave quantum critical point in ZrTe(3-x)Sex

It was found that selenium doping can suppress the charge-density-wave（CDW） order and induce bulk superconductivity in ZrTe3. The observed superconducting dome suggests the existence of a CDW quantum critical point（QCP） in ZrTe3-xSex near x ≈ 0.04. To elucidate the superconducting state near the CDW QCP, we measure the thermal conductivity of two ZrTe（3-x）Sex single crystals（x = 0.044 and 0.051） down to 80 m K. For both samples, the residual linear term κ0/T at zero field is negligible, which is a clear evidence for nodeless superconducting gap. Furthermore, the field dependence of κ0/T manifests a multigap behavior. These results demonstrate multiple nodeless superconducting gaps in ZrTe（3-x）Sex,which indicates conventional superconductivity despite of the existence of a CDW QCP.

Enhanced Intertwined Spin and Charge Orders in the t–J Model in a Small J Case

The one-band t–J model captures strong correlations in cuprate high-temperature superconductors.It accounts for the various intertwined spin and charge orders,and the superconductivity in the phase diagrams.To see the correlation effect on the intertwined orders,we implement the density matrix renormalization group method to simulate the t–J model in a small J case with t/J=10,which is in a deeper Mott region than that with t/J?3 in cuprate superconducting compounds.We examine the results on a six-leg lattice with both the nearest and next-nearest-neighbor hoppings and antiferromagnetic coupling,and find the absence of superconductivity and enhanced intertwined spin and charge orders in the phase diagram.Besides the stripe phases,we find a new SDW+CDW phase in which the spin modulation is a(π,π)antiferromagnetism,while the wavelength of the charge modulation is shorter than that of the stripe phases.Our results suggest the enhanced intertwined orders and suppressed superconductivity in the deep Mott region.

1.3 GHz 9-cell高性能超导腔高阶模耦合器电磁及热分析研究

中国科学院高能物理研究所于2023年6月完成了高品质因数1.3 GHz超导加速模组研发,在国际上率先实现了中温退火高品质因数超导腔模组技术路线。模组中集成了八只经过中温退火工艺处理的1.3 GHz9-cell超导腔,在模组的测试过程中超导腔的高阶模耦合器温升异常,导致超导腔无法在高梯度下稳定工作。通过HFSS软件和CST软件中的微波仿真模块对高阶模耦合器进行电磁分析,再通过理论和Ansys Workbench软件对高阶模耦合器进行热仿真分析,并结合模组的高功率实验,找到了超导腔性能异常的原因,并对超导腔高阶模耦合器的冷却方式进行了进一步的优化,解决了模组中超导腔高梯度下的不稳定性。

Spectroscopic Evidence for an Additional Symmetry Breaking in the Nematic State of FeSe Superconductor

In iron-based superconductors,FeSe has the simplest crystal structure which consists solely of the basic building block,the FeSe layers,that dictates the superconductivity.It undergoes a structural phase transition at around 90 K to enter a nematic state but without a long-range magnetic order.So,FeSe is an ideal system to investigate the nematicity and superconducting mechanism in iron-based superconductors,It represents a unique system that superconductivity and nematicity coexist in the superconducting stale,giving rise to its distinct electronic structure and superconducting gap structure.

Anomalous spectral weight transfer in the nematic state of iron-selenide superconductor

Nematic phase intertwines closely with high-Tc superconductivity in iron-based superconductors.Its mechanism,which is closely related to the pairing mechanism of superconductivity,still remains controversial.Comprehensive characterization of the electronic state reconstruction in the nematic phase is thus crucial.However,most experiments focus only on the reconstruction of band dispersions.Another important characteristic of electronic state,the spectral weight,has not been studied in details so far.Here,we studied the spectral weight transfer in the nematic phase of FeSe0.9S0.1 using angle-resolved photoemission spectroscopy and in-situ detwinning technique.There are two elliptical electron pockets overlapping with each other orthogonally at the Brillouin zone corner.We found that,upon cooling,one electron pocket loses spectral weight and fades away,while the other electron pocket gains spectral weight and becomes pronounced.Our results show that the symmetry breaking of the electronic state is manifested by not only the anisotropic band dispersion but also the band-selective modulation of the spectral weight.Our observation completes our understanding of the nematic electronic state,and put strong constraints on the theoretical models.It further provides crucial clues to understand the gap anisotropy and orbital-selective pairing in iron-selenide superconductors.

Theoretical Study on the Effect of Multiband Structure on Critical Temperature and Electronic Specific Heat in SmOFeAs Iron Pnictide Superconductor

In the present theoretical work, superconducting order parameter (∆) and electronic specific heat (Ces) of SmOFeAs iron pnictide (IP) superconductor has been studied using multiband (MB) model of IP superconductors. Attempt has been made to use the MB structure of IP superconductors and expressions for critical temperature (Tc) and Ces are obtained, calculations being made for one, two and three bands of SmOFeAs. It has been found that MB results are close to the experimental value of Tc for this compound. Ces calculations show jump of 1.5 × 10-5 eV/atom K, 4 × 10-5 eV/atom K and 4 × 10-5 eV/atom K for one, two and three band models respectively. The study brings out the importance of MB structure in IPs, highlighting the fact that increasing the number of bands, increases Tc. The specific heat jump (∆C) does not correspond to the BCS value, thereby proving that IPs are unconventional in nature.

基于迈斯纳效应的二阶梯度计不平衡度调节方法

基于超导量子干涉器的磁场梯度计可在无磁屏蔽的噪声环境中测得高信噪比信号,可检测pT量级的心脏磁场。通过推导超导环与二阶梯度计天线的互感耦合关系,建立三维静磁场仿真模型,模拟得出超导环对梯度计不平衡度的调节范围为-0.73~0.78。平衡后的梯度计可有效抑制0.031 Hz~10 Hz频率范围内环境噪声的谐波分量。梯度计在无磁屏蔽环境中测量得到42.64 dB高信噪比的心磁信号,验证了超导环平衡方法的可靠性。

用于金属磁微量能计信号读出的两级SQUID放大电路研究

金属磁微量能计(Metallic Magnetic Calorimeter,MMC)是一种具有极高能量分辨率的低温光子探测器。它通过顺磁材料磁化率在低温下随温度急剧变化的特性来实现对光子能量的精确测量。金属磁微量能计通常使用超导量子干涉器进行信号读出。研究介绍了一种用于金属磁微量能计信号读出的两级超导量子干涉器电路。初级放大器的设计采用了二阶梯度计构型,测试结果显示该设计方案有效的抑制了环境噪声的干扰。在液氦温度下,两级放大电路在磁通锁定环模式下实现了27400 V/A的跨阻增益,白噪声水平达到11.5 pA/Hz^(1/2)。

Larger in-plane upper critical field and superconducting diode effect observed in topological superconductor candidate InNbS_(2)nanoribbons

Recently,the coexistence of topology and superconductivity has garnered considerable attention.Specifically,the dimensionality of these materials is crucial for the realization of topological quantum computation.However,the naturally grown materials,especially with one-dimensional feature that exhibits the coexistence of topology and superconductivity,still face challenges in terms of experimental realization and scalability,which hinders the fundamental research development and the potential to revolutionize quantum computing.Here,we report the first experimental synthesis of quasi-one-dimensional InNbS_(2)nanoribbons that exhibit the coexistence of topological order and superconductivity via a chemical vapor transport method.Especially,the inplane upper critical field of InNbS_(2)nanoribbons exceeds the Pauli paramagnetic limit by more than 2.2 times,which can be attributed to the enhanced spin-orbit coupling and the weakened interlayer interaction between the NbS_(2)layers induced by the insertion of In atoms,making InNbS_(2)exhibit spin-momentum locking similar to that of monolayer NbS_(2).Moreover,for the first time,we report the superconducting diode effect in a quasi-one-dimensional superconductor system without any inherent geometric imperfections.The measured maximum efficiency is manifested as 14%,observed atμ0H≈±60 mT,and we propose that the superconducting diode effect can potentially be attributed to the presence of the nontrivial topological band.Our work provides a platform for studying exotic phenomena in condensed matter physics and potential applications in quantum computing and quantum information processing.

Theoretical understanding of correlation between magnetic phase transition and the superconducting dome in high-Tc cuprates

Many issues concerning the origin of high-temperature superconductivity(HTS)are still under debate.For example,how the magnetic order varies with doping and its relationship with the superconducting temperature(Tc);and why Tcalways peaks near the quantum critical point.In this paper,taking hole-doped La_(2)CuO_(4)as a classical example,we employ the first-principles band structure and total energy calculations with Monte Carlo simulations to explore how the symmetry-breaking magnetic ground state evolves with hole doping and the origin of a dome-shaped superconductivity region in the phase diagram.We demonstrate that the local antiferromagnetic order and doping play key roles in determining the electron-phonon coupling,thus Tc.Initially,the La_(2)CuO_(4)possesses a checkerboard local antiferromagnetic ground state.As the hole doping increases,Tcincreases with the enhanced electron-phonon coupling strength.But as the doping increases further,the strength of the antiferromagnetic interaction weakens and spin fluctuation increases.At the critical doping level,a magnetic phase transition occurs that reduces the local antiferromagnetism-assisted electron-phonon coupling,thus diminishing the Tc.The superconductivity disappears in the heavily overdoped region when the ferromagnetic order dominates.These observations could account for why cuprates have a dome-shaped superconductivity region in the phase diagram.Our study,thus,contributes to a fundamental understanding of the correlation between doping,local magnetic order,and superconductivity of HTS.

重费米子超导与竞争序

与其他非常规超导系列相比,重费米子超导体往往具有丰富多样的竞争序,超导与各种竞争序相伴而生,电子配对与反铁磁涨落、铁磁涨落、价态涨落、电四极矩涨落等量子临界涨落密切相关,扩充了非常规超导的研究内容.重费米子材料中的f电子往往同时参与超导与各种竞争序的形成,表现出局域与巡游的二重性.重费米子二流体理论为理解重费米子超导与竞争序的关系提供了新的思路.

超导磁储能系统自适应分数阶滑模控制设计

针对脉宽调制电流源型换流器(pulse-width modulated current source converter,PWM-CSC)的超导磁储能(superconducting magnetic energy storage,SMES)系统,设计了一款自适应分数阶滑模控制(adaptive fractional-order sliding-mode control,AFOSMC)策略。首先,将SMES系统的非线性、参数不确定性、未建模动态、以及外部扰动聚合成一个广义扰动,并利用滑模状态扰动观测器(sliding-mode state and perturbation observer,SMSPO)在线估计该扰动值。随后,通过分数阶滑模控制(fractional-order sliding-mode control,FOSMC)实时地对该扰动进行完全补偿,从而显著提高SMES系统的鲁棒性并获得全局一致的控制性能。同时,AFOSMC仅需测量SMES系统的d-q轴电流,并且采用扰动的实时估计值替代上限值进行补偿,因而其易于实现且具有更为合理的控制成本。该文进行了4种算例研究,即:1)有功功率和无功功率调节;2)电网故障下的系统恢复;3)新能源接入的功率波动平抑;4)参数不确定时的鲁棒性。仿真结果表明,AFOSMC相较于其他算法,具有最强的鲁棒性和最佳的动态响应性能。最后,基于dSpace的硬件在环(hardware-in-loop,HIL)实验验证了其硬件可行性。

10T超导强磁场下低温中和法制备有序亚微米Mn_xO_y的研究

利用XRD和TEM对无磁场和10T超导强磁场下低温中和法制备的试样进行了分析,结果表明:无磁场下,锰的沉淀物主要是锰的纳米氢氧化物;10T超导强磁场下,锰的沉淀物主要是锰的纳米水合氧化物。此外,10T超导强磁场对锰的纳米水合氧化物结晶度几乎没有影响。此外,对0T磁场和10T超导强磁场下制备试样在无磁场中进行经热处理后,利用XRD、SEM和Raman光谱分析仪对热处理试样进行了分析,结果表明:前者制备出了无序结构的亚微米MnxOy,后者制备出了有序结构的亚微米MnxOy,并且,有序亚微米MnxOy粒度分布更加均匀,但其活性却有所降低。

外磁场中超导网络相变的基本方程及其应用

本文从Ｇｉｎｚｂｕｒｇ－Ｌａｎｄａｕ方程（简称Ｇ—Ｌ方程）出发，导出了外磁场中细导线超导网络相变的基本方程。

基于超导HEB混频器的太赫兹超宽带耦合电路设计

超导HEB(Hot Electron Bolometer)热电子混频器是1THz以上灵敏度最高的相干探测器,为了进一步提高其灵敏度,有效减小射频信号在传输路径中的损耗,实现超导HEB混频器的超宽带混频功能,设计高耦合效率的射频匹配电路尤为重要。首先提出了混频器耦合电路的理论模型,然后采用三维电磁场仿真软件HFSS和类似于准光学天线的集总源法,设计了一种超宽带、低损耗的太赫兹信号耦合电路,对超导HEB混频器的嵌入阻抗在整个0.9～1.3THz的工作频带范围内进行了详细的分析。系统研究了低通滤波器中高低阻抗线结构,波导到微带转换中存在的高次模对射频信号传输的影响,并模拟仿真了实验中可能出现的磨片厚度误差对嵌入阻抗的影响。分析结果表明,该混频器的嵌入阻抗为35Ω-j10Ω左右,在整个工作频带内变化缓慢,能够实现超宽频带匹配,混频器的相对工作带宽可达到36%,仿真结果和理论模型计算结果完全一致。该研究结果对研制超宽带高灵敏度的超导HEB混频器具有很好的指导意义。

t-J模型中的超导长程序(英文)

严格证明了在任何非零温度下一维和二维窄带 (包括次近邻跳跃等 )t J模型不会呈现出S波最近邻配对、推广的 η配对、广义的离位Q配对和dx2 - y2 波配对的超导长程序 .如果在系统的电荷激发谱中存在一个激发能隙 ,则这些配对长程序在零温下也会被排除掉 .我们的结果对任意的J值和任意电子填充都成立 .