On similar lines as Is there an option to change the space/distance between tick labels and axes labels for plots? but I would like to reduce the distance between the tick mark and the tick label that appears below it. For eg:
In this figure, I would like to reduce the distance between -2 in the x axis and the tick mark corresponding to it 
Edit:
Adding the code that generated this figure:
cutoff = 0.52; grp1 = {{-4.10855, 1}, {-3.18, 2}, {-2.97477, 3}, {-2.40408, 4}, {-2.19854, 5}, {-1.77951, 6}, {-1.76863, 7}, {-1.75573, 8}, {-1.71227, 9}, {-1.64262, 10}, {-1.48712, 11}, {-1.42243, 12}, {-1.29815, 13}, {-1.18774, 14}, {-1.03156, 15}, {-0.978796, 16}, {-0.971106, 17}, {-0.922292, 18}, {-0.862833, 19}, {-0.807821, 20}, {-0.775937, 21}, {-0.750941, 22}, {-0.737334, 23}, {-0.715059, 24}, {-0.712102, 25}, {-0.693181, 26}, {-0.69129, 27}, {-0.674491, 28}, {-0.644356, 29}, {-0.620938, 30}, {-0.59347, 31}, {-0.589228, 32}, {-0.581852, 33}, {-0.580016, 34}, {-0.56826, 35}, {-0.566551, 36}, {-0.561733, 37}, {-0.55583, 38}, {-0.551104, 39}, {-0.549835, 40}, {-0.535232, 41}, {-0.53486, 42}, {-0.533395, 43}, {-0.523652, 44}, {-0.520547, 45}, {-0.508359, 46}, {-0.506626, 47}, {-0.491825, 48}, {-0.490019, 49}, {-0.477, 50}, {-0.473228, 51}, {-0.470723, 52}, {-0.470415, 53}, {-0.454857, 54}, {-0.454278, 55}, {-0.452099, 56}, {-0.421126, 57}, {-0.41768, 58}, {-0.415444, 59}, {-0.402139, 60}, {-0.387403, 61}, {-0.380952, 62}, {-0.374082, 63}, {-0.373277, 64}, {-0.370055, 65}, {-0.364634, 66}, {-0.361553, 67}, {-0.361208, 68}, {-0.360869, 69}, {-0.34248, 70}, {-0.340748, 71}, {-0.33172, 72}, {-0.330729, 73}, {-0.311965, 74}, {-0.310625, 75}, {-0.304104, 76}, {-0.302831, 77}, {-0.302533, 78}, {-0.29397, 79}, {-0.291521, 80}, {-0.289982, 81}, {-0.27621, 82}, {-0.264455, 83}, {-0.256689, 84}, {-0.250929, 85}, {-0.246889, 86}, {-0.228836, 87}, {-0.22671, 88}, {-0.202538, 89}, {-0.196612, 90}, {-0.187845, 91}, {-0.187817, 92}, {-0.179211, 93}, {-0.173247, 94}, {-0.165728, 95}, {-0.163806, 96}, {-0.153261, 97}, {-0.132747, 98}, {-0.122831, 99}, {-0.117507, 100}, {-0.113069, 101}, {-0.102309, 102}, {-0.0976552, 103}, {-0.0951561, 104}, {-0.0894875, 105}, {-0.0876338, 106}, {-0.087434, 107}, {-0.0845464, 108}, {-0.0757364, 109}, {-0.0635816, 110}, {-0.0621387, 111}, {-0.0580457, 112}, {-0.0558367, 113}, {-0.0529842, 114}, {-0.0478612, 115}, {-0.0444608, 116}, {-0.0410887, 117}, {-0.0398071, 118}, {-0.0322021, 119}, {-0.0200628, 120}, {-0.0182955, 121}, {-0.0144614, 122}, {-0.0138035, 123}, {-0.00716598, 124}, {0., 125}, {0.0103846, 126}, {0.0205011, 127}, {0.0341349, 128}, {0.059813, 129}, {0.0954803, 130}, {0.123192, 131}, {0.123591, 132}, {0.147797, 133}, {0.166342, 134}, {0.16952, 135}, {0.186956, 136}, {0.206183, 137}, {0.210853, 138}, {0.260639, 139}, {0.287231, 140}, {0.30835, 141}, {0.314636, 142}, {0.329798, 143}, {0.334356, 144}, {0.36056, 145}, {0.383386, 146}, {0.45576, 147}, {0.457104, 148}, {0.46041, 149}, {0.482364, 150}}; grp2 = {{0.559846, 151}, {0.603893, 152}, {0.692402, 153}, {0.736425, 154}, {0.742579, 155}, {0.750076, 156}, {0.879458, 157}, {0.967285, 158}, {0.988934, 159}, {1.04353, 160}, {1.06206, 161}, {1.12605, 162}, {1.13691, 163}, {1.14313, 164}, {1.22551, 165}, {1.24425, 166}, {1.32567, 167}, {1.35547, 168}, {1.3873, 169}, {1.46251, 170}, {1.48027, 171}, {1.48587, 172}, {1.50248, 173}, {1.50557, 174}, {1.52349, 175}, {1.52676, 176}, {1.61266, 177}, {1.6306, 178}, {1.71358, 179}, {1.73984, 180}, {1.79301, 181}, {1.81201, 182}, {1.86031, 183}, {1.90378, 184}, {1.91104, 185}, {1.932, 186}, {1.94978, 187}, {1.96444, 188}, {1.97321, 189}, {1.98785, 190}, {1.99161, 191}, {2.02637, 192}, {2.04347, 193}, {2.05299, 194}, {2.07511, 195}, {2.08866, 196}, {2.17186, 197}, {2.19635, 198}, {2.2132, 199}, {2.22343, 200}, {2.22452, 201}, {2.24434, 202}, {2.25782, 203}, {2.2627, 204}, {2.27745, 205}, {2.46167, 206}, {2.48096, 207}, {2.54055, 208}, {2.64996, 209}, {2.65934, 210}, {2.73535, 211}, {2.78724, 212}, {2.79484, 213}, {2.79819, 214}, {2.88538, 215}, {2.89362, 216}, {2.96651, 217}, {3.00729, 218}, {3.07063, 219}, {3.11961, 220}, {3.19508, 221}, {3.2295, 222}, {3.23329, 223}, {3.27631, 224}, {3.3876, 225}, {3.41121, 226}, {3.46174, 227}, {3.61129, 228}, {3.61579, 229}, {3.64525, 230}, {3.77605, 231}, {3.91162, 232}, {3.91579, 233}, {3.9266, 234}, {4.12641, 235}, {4.15509, 236}, {4.21151, 237}, {4.25269, 238}, {4.41959, 239}, {4.4295, 240}, {4.45912, 241}, {4.70492, 242}, {4.72227, 243}, {4.93772, 244}, {5.7519, 245}, {5.92314, 246}, {6.20269, 247}, {6.23834, 248}, {7.70686, 249}}; Show[ListPlot[{grp1, grp2}, Frame -> True, FrameLabel -> {Column[{Style["x", FontFamily -> "Courier"], Style["y", FontFamily -> "Courier"]}, Center], "(b) z", None, None, None}, AspectRatio -> 1.8, PlotStyle -> {{Blue, PointSize[0.01]}, {Red, PointSize[0.01]}}, FrameTicks -> {{{-2, -2, {0, 0.03}}, {0, 0, {0, 0.03}}, {cutoff, " " <> ToString[N[Round[cutoff, 10^-1]]], {0, 0.03}}, {2, 2, {0, 0.03}}, {4, 4, {0, 0.03}}, {6, 6, {0, 0.03}}}, {{1, 1, {0, 0.03}}, {50, 50, {0, 0.03}}, {100, 100, {0, 0.03}}, {150, 150, {0, 0.03}}, {200, 200, {0, 0.03}}}, None, None}, AxesOrigin -> {1, 0}, Axes -> False, ImageSize -> {211, 335}, ImagePadding -> {{50, 0}, {50, 0}}, PlotRange -> {{Automatic, Automatic}, {1, 250}}], Graphics[{Dashed, Black, Line[{{cutoff, 1}, {cutoff, 249}}]}]] 

