arXiv subjects

Sanjay Bachhar

Publications and source records attributed to Sanjay Bachhar.

5 recordsLinked to original sources

arXiv2025

Observation of a gapped phase in the one-dimensional $S = {\frac{1}{2}}$ Heisenberg antiferromagnetic chain Cu(Ampy)ClBr

Spin-1/2 Heisenberg antiferromagnetic frustrated spin chain systems display exotic ground states with unconventional excitations and distinct quantum phase transitions as the ratio of next-nearest-neighbor to nearest-neighbor coupling is tuned. We present a comprehensive investigation of the structural, magnetic, and thermodynamics properties of the spin-1/2 compound, Cu(Ampy)ClBr (Ampy= C$_6$H$_8$N$_2$ = 2-(Aminomethyl)pyridine) via x-ray diffraction, magnetization, specific heat, $^1$H nuclear magnetic resonance (NMR), electron spin resonance (ESR), and muon spin relaxation ($\mu$SR) techniques. The crystal structure features an anisotropic triangular chain lattice of magnetic Cu$^{2+}$ ions. Our bulk and local probe experiments detect neither long-range magnetic ordering nor spin freezing down to 0.06 K despite the presence of moderate antiferromagnetic interaction between Cu$^{2+}$ spins as reflected by a Curie-Weiss temperature of about $-9$ K from the bulk susceptibility data. A broad maximum is observed at about 9 K in magnetic susceptibility and specific heat data, indicating the onset of short-range spin correlations. At low temperatures, the zero-field magnetic specific heat and the $^1$H NMR spin-lattice relaxation rate follow an exponential temperature dependence, indicating the presence of gapped magnetic excitations. Furthermore, persistent spin dynamics down to 0.088 K observed by zero-field $\mu$SR evidences lack of any static magnetism.

cond-mat.str-el↗

arXiv2025

Effects of Ru-doping on the magnetism of Ag3LiIr2O6, a candidate Kitaev quantum spin liquid

We report our investigations on Ag3LiIr1.4Ru0.6O6, which results from the Ru substitution in the Kitaev quantum spin liquid candidate Ag3LiIr2O6. It crystallizes in the monoclinic C2/m space group like its parent compound, Ag3LiIr2O6. Our susceptibility measurements reveal an effective moment = 2.6 muB, which is higher than the moments of the parent compound and less than that of the Ru-analog (Ag3LiRu2O6), suggesting the presence of magnetic Ir4+ (Jeff= 1/2) and Ru4+ (S=1). Bulk magnetic susceptibility suggests long-range order (LRO)at T~20 K, whereas no clear signature is present in the heat capacity. Likewise, there is a loss of the 7Li NMR spectral intensity around T~20 K as expected at the onset of LRO, but a complete wipe-out is not seen in contrast to the result in Ag3LiIr2O6. There is also a T~20 K anomaly in the 7Li NMR relaxation rate and also a fall in the 7Li NMR shift with decreasing temperature. These results suggest LRO at T~20 K in Ag3LiIr1.4Ru0.6O6. However, at low-T below 10 K, we observe a power law variation in magnetic heat capacity and spin lattice relaxation rate, temperature-independent-7K, and no further loss of the 7Li NMR spectral intensity. These results might suggest the persistence or stabilisation of a quantum spin liquid-like phase, perhaps from a fraction of the sample in Ag3LiIr1.4Ru0.6O6 below 10 K. Our muon spin relaxation measurements suggest ordering around 20 K, consistent with our other probes. It appears that the main effect of Ru-substitution is to shift the LRO to a higher temperature in comparison with Ag3LiIr2O6, though there are signatures of a novel phase below about 10 K.

cond-mat.str-el↗

arXiv2025

A novel Gapless Quantum Spin Liquid in the S = 1 4d4-honeycomb material Cu$_3$LiRu$_2$O$_6$

We report the discovery of a novel gapless quantum spin liquid in the S=1 honeycomb system Cu$_3$LiRu$_2$O$_6$ with Ru$^{4+}$ ($4d^4$) where moments remain dynamic down to 50 mK. Heat capacity measurements show no sign of magnetic ordering down to 60 mK in spite of a Curie-Weiss temperature = -222 K indicating a strong antiferromagnetic interaction. In zero field, magnetic heat capacity shows a linear T-dependence with Sommerfeld coefficient = 107 mJ/mol K$^2$ is much larger than that found in typical Fermi liquids. Our local probe $^7$Li nuclear magnetic resonance (NMR) measurements find a significant temperature-independent $^7$Li NMR shift (and hence a non-zero spin susceptibility) at low-T and a linear T-variation of the $^7$Li NMR spin-lattice relaxation rate 1/T$_1$ at low-T reminiscent of fermionic excitations. Muon spin relaxation measurements detect neither long-range ordering nor spin freezing down to 50 mK and the temperature variation of the muon depolarization rate shows a gradual increase with decreasing temperature and a leveling off below about 1 K evincing a persistent spin dynamics common to several spin liquid candidates. Our results provide strong signatures of a quantum spin liquid in the titled honeycomb material.

cond-mat.str-el↗

arXiv2024

(H,Li)$_{6}$Ru$_{2}$O$_{6}$ : a possible zero-field Ru$^{3+}$-based Kitaev Quantum Spin Liquid

We report the synthesis and properties of (H,Li)$_{6}$Ru$_{2}$O$_{6}$, which is shown to be a $J_{\text{eff}}=\frac{1}{2}$ system made out of Ru$^{3+}$ moments in a honeycomb geometry. Bulk magnetization, heat capacity, nuclear magnetic resonance (NMR), and muon spin relaxation ($\mu$SR) rule out the presence of static moments or any spin glass phase down to 84 mK. All techniques suggest a crossover to a liquid-like state below about 40 K. The $^{7}$Li nuclear magnetic resonance (NMR) shift data suggest a non-zero $T$-independent spin susceptibility at low $T$. In zero field, $C_m/T$ shows $T^{-0.9}$ divergence which is consistent with vacancy-induced effects on low-energy excitations of the pristine Kitaev spin liquid. With field, power-law variations in the $^{7}$Li NMR spin-lattice relaxation rate 1/T$_{1}$ and magnetic heat capacity $C_{m}$ show quantitatively new scaling behaviors. A two-step entropy release in heat capacity is also observed putatively from $Z_{2}$ flux (low-$T$ step) and itinerant Majorana fermions (high-$T$ step). Based on these findings, we propose that (H,Li)$_{6}$Ru$_{2}$O$_{6}$ realizes a Kitaev spin liquid with no evidence of inherent magnetic ordering in zero field unlike $\alpha$-RuCl$_{3}$ where approximately $8$ Tesla field is required to suppress magnetic order.

cond-mat.str-el↗

arXiv2021

Unusual spin dynamics in the low-temperature magnetically ordered state of Ag$_{3}$LiIr$_{2}$O$_{6}$

Recently, there have been contrary claims of Kitaev spin-liquid behaviour and ordered behavior in the honeycomb compound Ag$_3$LiIr$_2$O$_6$ based on various experimental signatures. Our investigations on this system reveal a low-temperature ordered state with persistent dynamics down to the lowest temperatures. Magnetic order is confirmed by clear oscillations in the muon spin relaxation ($μ$SR) time spectrum below 9 K till 52 mK. Coincidentally in $^7$Li nuclear magnetic resonance, a wipe-out of the signal is observed below $\sim$ 10 K which again strongly indicates magnetic order in the low temperature regime. This is supported by our density functional theory calculations which show an appreciable Heisenberg exchange term in the spin Hamiltonian that favors magnetic ordering. The $^7$Li shift and spin-lattice relaxation rate also show anomalies at $\sim$ 50 K. They are likely related to the onset of dynamic magnetic correlations, but their origin is not completely clear. Detailed analysis of our $μ$SR data is consistent with a co-existence of incommensurate Néel and striped environments. A significant and undiminished dynamical relaxation rate ($\sim 5$ MHz) as seen in $μ$SR deep into the ordered phase indicates enhanced quantum fluctuations in the ordered state.

cond-mat.str-el↗