The $S=1/2$ spin ladder compound (C$_5$H$_{12}$N)$_2$CuBr$_4$ (BPCB) is studied by means of high-resolution inelastic neutron scattering. In agreement with previous studies we find a band of triplet excitations with a spin gap of $\sim0.8$~meV and a bandwidth of $\sim0.6$~meV. In addition, we observe a distinct splitting of the triplet band of $50(1)$~$μ$eV or $40(2)$~$μ$eV at the band minimum or maximum, respectively. By comparison to a strong coupling expansion calculation of the triplet dispersion for a spin ladder with anisotropic exchange, weakly anisotropic leg interactions are identified as the dominant source of magnetic anisotropy in BPCB. Based on these results, we discuss the nature of magnetic exchange anisotropy in BPCB and in related transition-metal insulators.
Polarized inelastic neutron scattering experiments recently identified the amplitude (Higgs) mode in C$_9$H$_{18}$N$_2$CuBr$_4$, a two-dimensional near-quantum-critical spin-1/2 two-leg ladder compound, which exhibits a weak easy-axis exchange anisotropy. Here, we theoretically examine the dynamic spin structure factor of such planar coupled spin-ladder systems using large-scale quantum Monte Carlo simulations. This allows us to provide a quantitative account of the experimental neutron scattering data within a consistent quantum spin model. Moreover, we trance the details of the continuous ev…
Spinon localization in the heat transport of the spin-1/2 ladder compound (C$_5$H$_{12}$N)$_2$CuBr$_4$
本文报道了自旋为1/2的梯形体系（C $_5$ H $_{12}$ N）$_2$ CuBr $_4$中磁场依赖的热输运性质.的热导率$κ(B)$是只有微弱的影响，由场诱导之间的无间隙的Luttinger液体状态实现的$B_{c1}< B < B_{c2}$和有间隙的状态，这表明没有一个直接的贡献的自旋激发的热传输。然而，我们观察到的热导率强烈抑制的磁场深处的Luttinger液体状态。这些令人惊讶的观察进行了讨论，在有限的阶梯段和自旋声子umklapp散射的主要声子热输运的自旋子的本地化。
Spin-spin correlations of the spin-ladder compound (C$_5$H$_{12}$N)$_2$CuBr$_4$ measured by magnetostriction and comparison to Quantum Monte Carlo results
详细分析了自旋梯型化合物哌啶溴化铜（C $_5$ H $_{12}$ N）$_2$ CuBr $_4$的磁致伸缩和热膨胀。我们发现完美的协议之间的实验和理论的两个腿的自旋阶梯哈密顿超过十年的温度和在很宽的磁场范围。将不同晶向的磁致伸缩与两个静态自旋-自旋关联函数联系起来，用量子蒙特卡罗方法计算了（C $_5$ H $_{12}$ N）$_2$ CuBr $_4$的磁弹性耦合.我们特别关注两个临界磁场$H_{c1}$和$H_{c2}$附近的量子临界行为，其特征在于源于临界自旋系统的低维性的强奇异性。扩展我们在Lorenz等人[Phys. Rev. Lett.，100，067208（2008）]，我们明确表明，上临界场$H_{c2}$附近的热膨胀是定量描述的一维，非相对论性费米子的无参数理论。我们还指出弹性模量存在奇异量子临界修正。这种校正与磁化率$χ$成比例，其在临界场处发散为$χ\sim 1/\sqrt{T}$，从而导致晶体的强烈软化。
We present the results of muon-spin spectroscopy ($μ^{+}$SR) measurements on the molecular spin ladder system (Hpip)$_{2}$CuBr$_{4(1-x)}$Cl$_{4x}$, [Hpip=(C$_{5}$H$_{12}$N)]. Using transverse field $μ^{+}$SR we are able to identify characteristic behaviour in each of the regions of the phase diagram of the $x=0$ strong-rung spin ladder system (Hpip)$_{2}$CuBr$_4$. Comparison of our results to those of the dimer-based molecular magnet Cu(pyz)(gly)(ClO$_{4}$) shows several common features. We locate the crossovers in partially disordered (Hpip)$_{2}$CuBr$_{4(1-x)}$Cl$_{4x}$ ($x=0.05$), where a r…
We report low temperature electron spin resonance experimental and theoretical studies of an archetype $S=1/2$ strong-rung spin ladder material (C$_{5}$H$_{12}$N)$_{2}$CuBr$_{4}$. Unexpected dynamics is detected deep in the Tomonaga-Luttinger spin liquid regime. Close to the point where the system is half-magnetized (and believed to be equivalent to a gapless easy plane chain in zero field) we observed orientation-dependent spin gap and anomalous $g$-factor values. Field theoretical analysis demonstrates that the observed low-energy excitation modes in magnetized (C$_{5}$H$_{12}$N)$_{2}$CuBr$_…
Quantum phase transitions in quantum matter occur at zero temperature between distinct ground states by tuning a nonthermal control parameter. Often, they can be accurately described within the Landau theory of phase transitions, similarly to conventional thermal phase transitions. However, this picture can break down under certain circumstances. Here, we present a comprehensive study of the effect of hydrostatic pressure on the magnetic structure and spin dynamics of the spin-1/2 ladder compound C$_9$H$_{18}$N$_2$CuBr$_4$. Single-crystal heat capacity and neutron diffraction measurements reve…
We address quantum spin helical states in the strongly frustrated Heisenberg model. Contrary to conventional Dzyaloshinskii-Moriya approach we show that such states appear without central symmetry breaking. As an example, we demonstrate that the magnetic and thermodynamic properties of the quasi-two-dimensional square-lattice compound $\mathrm{(CuBr)Sr_{2}Nb_{3}O_{10}}$ can be interpreted within 2D $S = 1/2$ $J_1-J_2-J_3$ Heisenberg model. In this compound neutron experiment indicates helical spin order while central symmetry does hold.
Motivated by the intriguing mode splittings in a magnetic field recently observed with inelastic neutron scattering in the spin ladder compound (C$_5$H$_{12}$N)$_2$CuBr$_4$ (BPCB), we investigate the nature of the spin ladder excitations using DMRG and analytical arguments. Starting from the fully frustrated ladder, for which we derive the low-energy spectrum, we show that bound states are generically present close to $k=0$ in the dynamical structure factor of spin ladders above $H_{c 1}$, and that they are characterized by a field-independent binding energy and an intensity that grows with $H…
By means of inelastic neutron scattering we investigate finite temperature dynamics in the quantum spin ladder compound (C$_5$H$_{12}$N)$_2$CuBr$_4$ (BPCB) near the magnetic field induced quantum critical point with dynamical exponent $z=2$. We observe universal finite-temperature scaling of the transverse local dynamic structure factor in spectacular quantitative agreement with long-standing theoretical predictions. At the same time, already at rather low temperatures, we observe strong non-universal longitudinal fluctuations. To separate the two, we make use of an intrinsic leg-exchange symm…
Magnetic excitations in the strong-leg quantum spin ladder compound (C$_7$H$_{10}$N)$_2$CuBr$_4$ (known as DIMPY) in the field-induced Tomonaga-Luttinger spin liquid phase are studied by means of high-field electron spin resonance (ESR) spectroscopy. The presence of a gapped ESR mode with unusual non-linear frequency-field dependence is revealed experimentally. Using a combination of analytic and exact diagonalization methods, we compute the dynamical structure factor and identify this mode with longitudinal excitations in the antisymmetric channel. We argue that these excitations constitute a…
Atomic and magnetic structures of (CuCl)LaNb$_2$O$_7$ and (CuBr)LaNb$_2$O$_7$: Density functional calculations
用密度泛函方法研究了（Cu $X$）LaNb $_2$ O $_7$（$X$ =Cl和Br）的原子结构和磁性.在几十个被检查的结构中，正交畸变的$2\times 2$结构，其中$X$卤素的位移模式类似于先前基于经验信息所描述的模型，被确定为最稳定的一个。$X$卤素的置换与Cu离子的置换一起导致在两种材料中形成$X$ -Cu-$X$-Cu-$X$之字形链。Z字形链中的最近邻相互作用对（CuCl）LaNb $_2$ O $_7$是反铁磁的（AFM），而对（CuBr）LaNb $_2$ O $_7$是铁磁的（FM）.另一方面，前两个相邻的铜阳离子之间的相互作用从相邻的链被发现是AFM和FM分别为这两个化合物。在（CuBr）LaNb $_2$ O $_7$中所有这些面内交换耦合的大小被估计为在（CuCl）LaNb $_2$ O $_7$中的那些的大约三倍。此外，一个相当大的AFM面间相互作用被发现由两个NbO $_6$八面体分离的Cu离子之间。本研究强烈地表明，为了正确地解释（Cu $X)$ LaNb $_2$ O $_7$）的磁性，有必要超越正方形$J_1-J_2$模型。
Short-range order of Br and three-dimensional magnetism in (CuBr)LaNb2O7
我们提出了一个全面的研究（CuBr）LaNb 2 O 7的晶体结构，磁结构和微观磁模型，Br模拟的自旋能隙量子磁体（CuCl）LaNb 2 O 7。尽管晶体结构和自旋晶格相似，但Cl和Br化合物的磁性行为甚至原子排列的特殊性都非常不同。高分辨率的X射线和中子数据揭示了Br原子在（CuBr）LaNb 2 O 7中的分裂位置。这种分裂起源于两种可能的配置开发的[CuBr]锯齿带。虽然Br原子在'ab'平面中局部有序，但它们沿'c'方向的排列仍然部分无序。占主导地位的和积极的更有利的配置功能的“c”晶格参数，没有观察到（CuCl）LaNb 2 O 7的额外的两倍。（CuBr）LaNb 2 O 7在TN=32 K时发生了长程反铁磁有序化，约为J 4 ~48 K时的70%。Br化合物并没有表现出任何低维磁性的实验特征，因为底层的自旋晶格是三维的。沿'c'方向的耦合与'ab'平面中的耦合相当，尽管沿'c'方向的最短Cu-Cu距离（11.69 A）比'ab'平面中的最近邻距离（3.55 A）大三倍。实验证实了条纹反铁磁长程序的特点列的平行自旋在'ab'平面和反平行自旋沿'c'的实验和微观分析证实。
Unconventional Transition from Metallic to Insulating Resistivity in the Spin-ladder Compound (Sr,Ca)$_{14}$Cu$_{24}$O$_{41}$
自旋梯化合物是高温超导体有趣的类似物，因为它们含有由铜和氧原子组成的正方形阵列的近一维“梯”层。增加梯子中的腿的数量提供了一种逐步接近二维铜-氧平面的方法，该结构被认为是高温超导性的关键。短程自旋相关的阶梯已被预测，导致形成的空穴对有利于超导性，一旦足够的空穴被引入到阶梯上的掺杂。事实上，在高压下，在两腿梯形化合物（Sr，Ca）$_{14}$ Cu $_{24}$ O $_{41}$中已经发现了超导性。在这里，我们表明，在非超导状态下的（Sr，Ca）$_{14}$ Cu $_{24}$ O $_{41}$共享三个不同的制度，在共同的高温超导体，包括一个无法解释的绝缘行为在低温下的电阻率增加的温度的对数。这些观察结果表明，对数发散来自一个新的本地化机制共同的梯形化合物和高温超导体，这可能是由于近一维的电荷输运在自旋间隙的存在。
We have measured the magnetization of the organic compound BIP-BNO (3,5'-bis(N-tert-butylaminoxyl)-3',5-dibromobiphenyl) up to 76 T where the magnetization is saturated. The S = 1/2 antiferromagnetic Heisenberg two-leg spin-ladder model accounts for the obtained experimental data regarding the magnetization curve, which is clarified using the quantum Monte Carlo method. The exchange constants on the rung and the side rail of the ladder are estimated to be J(rung)/kB = 65.7 K and J(leg)/kB = 14.1 K, respectively, deeply in the strong coupling region: J(rung)/J(leg) > 1.
Temperature and composition phase diagram in the iron-based ladder compounds Ba1-xCsxFe2Se3
研究了铁基梯形化合物（Ba，Cs）Fe $_2$ Se $_3$ .它们的母体化合物BaFe $_2$ Se $_3$和CsFe $_2$ Se $_3$具有不同的空间群、Fe的价态和磁性结构。通过电阻率、比热容、磁化率、X射线衍射和粉末中子衍射等测量，得到了该体系的温度和组成相图。在BaFe $_2$ Se $_3$中观察到的块磁性被Cs掺杂显著抑制。相比之下，在CsFe $_2$ Se $_3$中观察到的条带磁性对于Ba掺杂不是如此脆弱。在中间组分中出现了新的磁性结构，类似于CsFe $_2$ Se $_3$的条形磁性，但梯间自旋组态不同。中间化合物显示绝缘行为，然而有限的$T$ -线性贡献的比热在低温下获得。
The quasi-one-dimensional spin ladder compounds, BaFe$_2$S$_3$ and BaFe$_2$Se$_3$, are investigated by infrared spectroscopy and density functional theory (DFT) calculations. We observe strong anisotropic electronic properties and an optical gap in the leg direction that is gradually filled above the antiferromagnetic (afm) ordering temperature, turning the systems into a metallic phase. Combining the optical data with the DFT calculations we associate the optical gap feature with the $p$-$d$ transition that appears only in the afm ordered state. Hence, the insulating ground state along the le…
Since the discovery of pressure-induced superconductivity in the two-leg ladder system BaFe$_2X_3$ ($X$=S, Se), with the 3$d$ iron electronic density $n = 6$, the quasi-one-dimensional iron-based ladders have attracted considerable attention. Here, we use Density Functional Theory (DFT) to predict that the novel $n = 6$ iron ladder BaFe$_2$Te$_3$ could be stable with a similar crystal structure as BaFe$_2$Se$_3$. Our results also indicate that BaFe$_2$Te$_3$ will display the complex 2$\times$2 Block-type magnetic order. Due to the magnetic striction effects of this Block order, BaFe$_2$Te$_3$ …
The field induced quantum phase transitions in the disorder-free and disordered samples of the spin ladder material (CH_3)_2CHNH_3Cu(Cl_{1-x}Br_x)_3 are studied using magnetic calorimetry and magnetic neutron diffraction on single crystal samples. Drastically different critical indexes and correlation lengths in the high field phase are found for two different orientations of the applied field. It is argued that for a field applied along the crystallographic c axis, as in previous studies [1], the transition is best described as an Ising transition in random field and anisotropy, rather than a…
Magnetostrictive Neel ordering of the spin-5/2 ladder compound BaMn2O3: distortion-induced lifting of geometrical frustration
本文用热力学和衍射技术研究了BaMn $_2$ O $_3$的晶体结构和磁性。BaMn $_2$ O $_3$是$S = 5/2$自旋阶梯的实现，因为磁性相互作用沿着形成阶梯的腿和横档的180个$^\circ$ Mn-O-Mn键占主导地位。的磁化率的温度依赖性表现出良好定义的最大值为所有方向证明低维磁字符在BaMn $_2$ O $_3$。然而，磁化率和粉末中子衍射数据表明，BaMn $_2$ O $_3$在184 K时表现出向反铁磁有序的转变，尽管在正交高温相中最近邻的梯间耦合完全受挫。这种挫败感被伴随着磁性转变的非常强烈的单斜畸变所解除。
Electrical resistivity measurements have been performed on the iron-based ladder compounds Ba$_{1-x}$Cs$_x$Fe$_2$Se$_3$ ($x$ = 0, 0.25, 0.65, and 1) under high pressure. A cubic anvil press was used up to 8.0 GPa, whereas further higher pressure was applied using a diamond anvil cell up to 30.0 GPa. Metallic behavior of the electrical conductivity was confirmed in the $x$ = 0.25 and 0.65 samples for pressures greater than 11.3 and 14.4 GPa, respectively, with the low-temperature $\log T$ upturn being consistent with weak localization of 2D electrons due to random potential. At pressures higher…
Magnetotransport Properties of Iron-Based Ladder Compounds BaFe2S3 and BaFe2Se3 under High Pressure
Graduate School of Advanced Science and Engineering, Hiroshima University（广岛大学高级科学与工程学院）；International Institute for Sustainability with Knotted Chiral Meta Matter (WPI-SKCM2), Hiroshima University（广岛大学螺旋手性超材料可持续性国际研究所）；Department of Physics, Graduate School of Science, Tohoku University（东北大学理学院物理系）
Experimental evidence of paired hole states in model high-$T_c$ compounds
本文用半经验的X射线吸收（XAS）再分析和精确对角化的团簇计算重新研究了Sr $_{14-x}$ Ca $_x$ Cu $_{24}$ O $_{41}$（SCCO）中空穴的分布。一个新的解释XAS数据导致更大的阶梯孔密度比以前建议。这些新的空穴密度导致最近报道的空穴晶体（HC）沿阶梯1/3和1/5波矢量的简单解释。我们的解释与梯子横档上的成对孔是一致的。对掺杂阶梯结构的极小模型的精确对角化结果表明，由于共振价键（RVB）物理作用，由正方形格元中的4个自旋组成的自旋结构的稳定化抑制了具有1/4波矢的空穴晶体。
We report on a sequence of field-induced transitions in the zigzag ladder compound BaDy2O4 studied with powder neutron diffraction and magnetisation measurements. In agreement with the previously published results, the low temperature zero-field structure is characterised by two half-integer propagation vectors, k1=[1/2 0 1/2] and k2= 1/2 1/2 1/2]. However, on application of an external magnetic field, the Bragg peaks corresponding to the zero-field structure lose their intensity rather rapidly and disappear completely in a field of 2.5 kOe. In the intermediate fields, 2.5 to 22.5 kOe, new pea…
