Fermionic spin liquid analysis of the paramagnetic state in volborthite

Chern, Li Ern; Schaffer, Robert; Sorn, Sopheak; Kim, Yong Baek

doi:10.1103/physrevb.96.165117

Cited by 8 publications

(10 citation statements)

References 39 publications

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“…While no clear non-zero κ 0 /T term was observed for Volborthite due to its relatively high ordering temperature, the estimated mean free path of the spin excitations from the 8 K magnetic thermal conductivity is about 80 times its inter-spin distance, which indicates its spin excitations are highly mobile 49 . The related theoretical work also proposes the existence of spinon Fermi surface in Volborthite above T N 50,51 . Another relevant example is pyrochlore Yb 2 Ti 2 O 7 with effective spin-1/2 Yb 3+ ions, which ferromagnetically orders at T C~0 .2 K 52 .…”

Section: Resultsmentioning

confidence: 97%

Possible itinerant excitations and quantum spin state transitions in the effective spin-1/2 triangular-lattice antiferromagnet Na2BaCo(PO4)2

Huang

Yue

et al. 2020

Nat Commun

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The most fascinating feature of certain two-dimensional (2D) gapless quantum spin liquid (QSL) is that their spinon excitations behave like the fermionic carriers of a paramagnetic metal. The spinon Fermi surface is then expected to produce a linear increase of the thermal conductivity with temperature that should manifest via a residual value (κ 0 /T) in the zerotemperature limit. However, this linear in T behavior has been reported for very few QSL candidates. Here, we studied the ultralow-temperature thermal conductivity of an effective spin-1/2 triangular QSL candidate Na 2 BaCo(PO 4) 2 , which has an antiferromagnetic order at very low temperature (T N~1 48 mK), and observed a finite κ 0 /T extrapolated from the data above T N. Moreover, while approaching zero temperature, it exhibits series of quantum spin state transitions with applied field along the c axis. These observations indicate that Na 2 BaCo (PO 4) 2 possibly behaves as a gapless QSL with itinerant spin excitations above T N and its strong quantum spin fluctuations persist below T N .

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Section: Resultsmentioning

confidence: 97%

Possible itinerant excitations and quantum spin state transitions in the effective spin-1/2 triangular-lattice antiferromagnet Na2BaCo(PO4)2

Huang

Yue

et al. 2020

Nat Commun

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“…where the elementary triangles that build up the kagome lattice are no longer equilateral but isosceles, leading to different antiferromagnetic couplings along short and long bonds. In this case, there is some evidence for a magnetic ground state, even though unusually slow spin fluctuations persist down to low temperatures [25][26][27][28][29][30][31][32][33]. Another interesting deformation is one leading to alternately sized equilateral triangles, dubbed the trimerized or breathing kagome lattice [34], in analogy to the breathing pyrochlores [35].…”

Section: Introductionmentioning

confidence: 99%

Persistence of the gapless spin liquid in the breathing kagome Heisenberg antiferromagnet

et al. 2018

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The nature of the ground state of the spin S = 1/2 Heisenberg antiferromagnet on the kagome lattice with breathing anisotropy (i.e., with different superexchange couplings J and J within elementary up-and downpointing triangles) is investigated within the framework of Gutzwiller projected fermionic wave functions and Monte Carlo methods. We analyze the stability of the U(1) Dirac spin liquid with respect to the presence of fermionic pairing that leads to a gapped Z2 spin liquid. For several values of the ratio J /J , the size scaling of the energy gain due to the pairing fields and the variational parameters are reported. Our results show that the energy gain of the gapped spin liquid with respect to the gapless state either vanishes for large enough system size or scales to zero in the thermodynamic limit. Similarly, the optimized pairing amplitudes (responsible for opening the spin gap) are shown to vanish in the thermodynamic limit. Our outcome is corroborated by the application of one and two Lanczos steps to the gapless and gapped wave functions, for which no energy gain of the gapped state is detected when improving the quality of the variational states. Finally, we discuss the competition with the "simplex" Z2 resonating-valence-bond spin liquid, valence-bond crystal, and nematic states in the strongly anisotropic regime, i.e., J J .arXiv:1712.04579v2 [cond-mat.str-el] 15 Mar 2018 J /J = 1 J /J = 0.9 J /J = 0.7 J /J = 0.5 J /J = 0.3 J /J = 0.1 Z of J ) in the strong anisotropy limit:FIG. 7. For different values of the breathing anisotropy J /J , the finite-size scaling of the energy gain (in units of J ) of the sixsite unit-cell VBC with respect to the U(1) Dirac spin liquid, i.e., [E(VBC)−E(U(1))]/J . The clusters considered are L = 8, 12, 16, and 20.

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“…The U (1) SL's with spinon Fermi surfaces are found as root states of many Z 2 fermionic SL's, when the spinon pairing amplitudes in the Z 2 states are turned off [45]. If spinon pairing that arises from the gauge-field mediated attractive interactions between spinons is considered, such states are susceptible to various pairing insta-bilities [11,19,21].…”

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confidence: 99%

Field-Induced Instability of a Gapless Spin Liquid with a Spinon Fermi Surface

et al. 2017

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The ground state of the quantum kagome antiferromagnet Zn-brochantite, ZnCu3(OH)6SO4, which is one of only a few known spin-liquid (SL) realizations in two or three dimensions, has been described as a gapless SL with a spinon Fermi surface. Employing nuclear magnetic resonance in a broad magnetic-field range down to millikelvin temperatures, we show that in applied magnetic fields this enigmatic state is intrinsically unstable against a SL with a full or a partial gap. A similar instability of the gapless Fermi-surface SL was previously encountered in an organic triangular-lattice antiferromagnet, suggesting a common destabilization mechanism that most likely arises from spinon pairing. A salient property of this instability is that an infinitesimal field suffices to induce it, as predicted theoretically for some other types of gapless SL's.Fermi-surface instability is one of the central concepts in condensed matter physics, responsible for diverse collective phenomena [1]. In metals, various symmetrybroken phases, e.g., the BCS superconducting, Peierls [2], electronic nematic [3, 4] and itinerant antiferromagnetic [5] states, occur due to such instabilities. An extension of the Fermi-liquid theory to Mott insulators leads to fermionic quantum spin liquids (SL's) [6]. These are intriguing disordered, yet highly entangled states of matter that are characterized by effective low-energy chargeneutral fermionic quasiparticles known as spinons, which interact through emergent gauge fields [6][7][8][9][10]. In analogy to the Fermi-surface instabilities in metals, many SL's with different symmetries may be considered as being born out of the SL with a spinon Fermi surface (dubbed a spinon metal) [11,12]. Since this parent state is gapless and thus exposed to perturbations and fluctuations, finding its rare realizations is challenging per se [6,13,14,16]. Moreover, clarifying the nature of its experimentally observed instabilities [1,17] by confronting numerous theoretical proposals [11,12,[19][20][21] with experimental facts represents an even greater challenge. Clearly, identifying some common origin of such instabilities would be beneficial for obtaining an in-depth understanding of the Fermi-surface instabilities in general.In this context, Zn-brochantite, ZnCu 3 (OH) 6 SO 4 , a representative of the paradigmatic two-dimensional geometrically frustrated quantum kagome antiferromagnet [7], is of particular interest. Around 10 K, well below the average nearest-neighbor exchange interaction J = 65 K [6], it exhibits a spinon Fermi-surface SL state with Pauli-like kagome-lattice magnetic susceptibility χ k and with specific heat c p increasing linearly with temperature [6]. Unexpectedly, this state progressively transforms when the temperature is lowered as χ k and c p /T get gradually enhanced and saturate at 2-3-times larger values below ∼0.6 K [6,22]. This state remains stable down to the lowest experimentally accessible temperatures (T /J 3 · 10 −4 ) [1]. The crossover within the spinon Fermi-surface SL state is l...

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Fermionic spin liquid analysis of the paramagnetic state in volborthite

Cited by 8 publications

References 39 publications

Possible itinerant excitations and quantum spin state transitions in the effective spin-1/2 triangular-lattice antiferromagnet Na2BaCo(PO4)2

Possible itinerant excitations and quantum spin state transitions in the effective spin-1/2 triangular-lattice antiferromagnet Na2BaCo(PO4)2

Persistence of the gapless spin liquid in the breathing kagome Heisenberg antiferromagnet

Field-Induced Instability of a Gapless Spin Liquid with a Spinon Fermi Surface

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