Quantum phase diagram of ferromagnetically coupled singlet dimers on a distorted Shastry-Sutherland lattice

Frustrated spin-1/2 model with all-antiferromagnetic exchange on Shastry-Sutherland lattice (SSL) has been extensively explored, and in this work we study the quantum phase diagram of isotropic Heisenberg spin- <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mn>1</a:mn> <a:mo>/</a:mo> <a:mn>2</a:mn> </a:mrow> </a:math> model on the SSL with ferromagnetic exchange interactions along leg, and antiferromagnetic couplings along the diagonal bonds ( <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mi>J</b:mi> </b:math> ). Using density matrix renormalization group (DMRG) and exact diagonalization calculations, we identify four distinct ground-state (gs) phases for this frustrated spin-1/2 model: stripe <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mrow> <c:mo>(</c:mo> <c:mi>π</c:mi> <c:mo>,</c:mo> <c:mn>0</c:mn> <c:mo>)</c:mo> </c:mrow> </c:math> , stripe <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:mrow> <d:mo>(</d:mo> <d:mn>0</d:mn> <d:mo>,</d:mo> <d:mi>π</d:mi> <d:mo>)</d:mo> </d:mrow> </d:math> , ferromagnetic, and spiral-dimer phases. In the spiral-dimer phase the gs can exhibit dimer formation along the diagonal bonds with or without spins spiral along the <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"> <e:mi>x</e:mi> </e:math> axis or <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"> <f:mi>y</f:mi> </f:math> axis in different parameter regime and these states are connected through crossovers. There is a continuous transition between stripe with a long-range spin-spin correlations and spiral-dimer phase with a short-range correlations. An effective spin parameter is introduced to accurately determine the phase boundaries. Our DMRG results differ significantly from previous Schwinger boson mean-field theory predictions. The spiral phase occurs in a narrow range of the parameter space and shows short-range correlations in the system.