Random singlet state in Ba5CuIr3O12 single crystals

Abstract

We study the thermodynamic and high-magnetic-field properties of the magnetic insulator Ba5CuIr3O12, which shows no magnetic order down to 2 K consistent with a spin liquid ground state. While the temperature dependence of the magnetic susceptibility and the specific heat shows only weak antiferromagnetic correlations, we find that the magnetization does not saturate up to a field of 59 Tesla, leading to an apparent contradiction. We demonstrate that the paradox can be resolved, and all of the experimental data can be consistently described within the framework of random singlet states. We demonstrate a generic procedure to derive the exchange coupling distribution P (J) from the magnetization measurements and use it to show that the experimental data is consistent with the power-law form P (J) ∼ J −α with α ≈ 0.6. Thus, we reveal that high-magnetic-field measurements can be essential to discern quantum spin liquid candidates from disorder dominated states that do not exhibit long-range order.Strong quantum fluctuations in insulating magnetic compounds can give rise to quantum spin liquid (QSL) ground states, where the interaction-driven ordering tendencies are thwarted completely. Devoid of long-range order, QSLs lie beyond the Landau symmetry-based classification, and are characterized instead by their unconventional entanglement properties and the presence of exotic fractionalized excitations [1,2]. However, identifying the elusive QSL behavior in real materials has proven to be a formidable task [2][3][4]. The search for QSL candidate materials represents a major challenge of modern condensed matter physics.Disorder is one of the major hindrances to identify QSL materials [5][6][7], as it can drive the formation of random singlet states (RSS) [8] or disordered stripe states [9] instead of a QSL. Importantly, this includes single-crystal samples due to intrinsic disorder [10,11]. A convenient reference point can be found in one-dimensional (1D) systems, where the quantum fluctuations are dominant [12] and the effect of disorder was clarified some time ago [13,14]. In 1D it converts the spin liquid ground state into a RSS, where the effective exchange coupling follows a broad probability distribution that has a universal form [15] at low energies. In 2D and 3D, on the contrary, the fate of disordered spin systems is still an open question. While a random singlet state with a power-law distribution has been conjectured [16], the true ground state of such systems is still under debate and might not be universal [17][18][19]. In particular, enhanced suppression of QSL states by disorder has been found in model calculations [19,20]. However, mechanisms for the stabilization of QSL states by disorder have also been proposed [21]. Additionally, a strong spin-orbit coupling (SOC) is an important ingredient in many QSL candidates. While its effects on clean QSLs have been studied [1, 2] and particularly emphasized for the so-called Kitaev materials [22,23], the interplay of SOC with disorder still remains to be underst...

Characterizing random-singlet state in two-dimensional frustrated quantum magnets and implications for the double perovskite Sr$_2$CuTe$_{1-x}$W$_{x}$O$_6$

“…The RS state consists of pairs of spin singlets, where the longrange singlets are much weaker than the short ones and the singlets cannot cross 25 . This state has been found universal for a broad class of 1d spin models with random couplings [27][28][29] and has been reported recently in spin-chain materials such as Ba 5 CuIr 3 O 12 30 and BaCu 2 (Si 1−x Ge x ) 2 O 31 .…”

Hexagonal Perovskites as Quantum Materials

“…Although weak antiferromagnetic interactions were seen in the magnetic susceptibility and heat capacity measurements, the magnetization did not saturate, even up to a 59 T applied magnetic field. This implies the existence of a random single state, which can fully explain the experimental data 213 . In contrast to the other materials described here, the crystal structure of Ca2IrO4 214 displays a pure 1D chain of edgesharing (not face-sharing) IrO6 octahedra, but nonetheless has hexagonal symmetry, as shown in Figure 34.…”

Non-magnetic ion site disorder effects on the quantum magnetism of a spin-1/2 equilateral triangular lattice antiferromagnet

“…Several theoretical models which include this site disorder effect have been proposed for YMGO: highly anisotropic nearest-neighbor interactions [12], the random singlet (RS) state [13,14], randomness-induced QSL state [15], the mimicry of a spin liquid [16,17], and randomness induced spin-liquid-like phase in J 1 -J 2 model [18][19][20][21][22][23][24]. Of these, the RS state and randomnessinduced QSL have also been applied to other quantum magnets with disorder [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43]. However, a most recent study on high quality YMGO single crystals reveals a residual κ 0 /T term and series of quantum spin state transitions at the zero temperature limit.…”